Loop structures for supporting multiple electrode elements

ABSTRACT

A catheter assembly comprises a sheath, which includes a side wall enclosing an interior bore, a distal region, and an opening in the sidewall. The assembly also comprises a bendable catheter tube, which is carried for sliding movement in the interior bore. The catheter tube has a distal portion. The assembly further comprises a coupling, which joins the distal region of the sheath and the distal portion of the catheter tube. The coupling causes bending of the catheter tube outwardly through the opening, in response to sliding movement of the catheter tube within the interior bore toward the distal region of the sheath.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of 09/017,465 filed on Feb. 2, 1998,now U.S. Pat. No. 6,071,274, which is a continuation-in-part ofco-pending U.S. application Ser. No. 08/769,856, filed Dec. 19, 1996.

FIELD OF THE INVENTION

The invention generally relates structures for supporting one or morediagnostic or therapeutic elements in contact with body tissue. In amore particular sense, the invention relates to structures well suitedfor supporting one or more electrode elements within the heart.

BACKGROUND OF THE INVENTION

The treatment of cardiac arrhythmias requires electrodes capable ofcreating tissue lesions having a diversity of different geometries andcharacteristics, depending upon the particular physiology of thearrhythmia to be treated.

For example, it is believed the treatment of atrial fibrillation andflutter requires the formation of continuous lesions of differentlengths and curvilinear shapes in heart tissue. These lesion patternsrequire the deployment within the heart of flexible ablating elementshaving multiple ablating regions. The formation of these lesions byablation can provide the same therapeutic benefits that the complexincision patterns that the surgical maze procedure presently provides,but without invasive, open heart surgery.

By way of another example, small and shallow lesions are desired in thesinus node for sinus node modifications, or along the A-V groove forvanous accessory pathway ablations, or along the slow zone of thetricuspid isthmus for atrial flutter (AFL) or AV node slow pathwaysablations. However, the elimination of ventricular tachycardia (VT)substrates is thought to require significantly larger and deeperlesions.

There also remains the need to create lesions having relatively largesurface areas with shallow depths.

The task is made more difficult because heart chambers vary in size fromindividual to individual. They also vary according to the condition ofthe patient. One common effect of heart disease is the enlargement ofthe heart chambers. For example, in a heart experiencing atrialfibrillation, the size of the atrium can be up to three times that of anormal atrium.

A need exists for electrode support structures that can create lesionsof different geometries and characteristics, and which can readily adoptto different contours and geometries within a body region, e.g., theheart.

SUMMARY OF THE INVENTION

The invention provides structures for supporting operative therapeuticor diagnostic elements within an interior body region, like the heart.The structures possess the requisite flexibility and maneuverabilitypermitting safe and easy introduction into the body region. Oncedeployed in the body region, the structures possess the capability toconform to different tissue contours and geometries to provide intimatecontact between the operative elements and tissue.

The invention provides a catheter assembly comprising a sheath, whichincludes a side wall enclosing an interior bore, a distal region, and anopening in the sidewall. The assembly also includes a bendable cathetertube, which is carried for sliding movement in the interior bore. Thecatheter tube has a distal portion. The assembly further comprises acoupling, which joins the distal region of the sheath and the distalportion of the catheter tube. The coupling causes bending of thecatheter tube outwardly through the opening, in response to slidingmovement of the catheter tube within the interior bore toward the distalregion of the sheath.

In one embodiment, bending of the catheter tube forms a loop, whichextends outwardly of the opening and which is supported near the sheathby the coupling. In this embodiment, the coupling comprises a flexiblejoint.

In one embodiment, the catheter tube carries at least one operativeelement, e.g., an electrode.

Other features and advantages of the inventions are set forth in thefollowing Description and Drawings, as well as in the appended Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a probe, which carries on its distalregion a multiple electrode support structure that embodies features ofthe invention;

FIG. 2A is an enlarged side view, with portions broken away and insection, of the distal region of the probe shown in FIG. 1;

FIG. 2B is a side view of the multiple electrode structure shown in FIG.1, in which stiffness is varied using a slidable, tapered spline leg;

FIG. 3A is an enlarged side view of the distal region of the probe shownin FIG. 1, showing the multiple electrode structure advanced from theassociated sheath to form a loop;

FIG. 3B is a perspective end view of an embodiment of the sheath shownin FIG. 3A, in which wires are placed to provide added torsionalstiffness;

FIG. 3C is an end view of an embodiment of the sheath shown in FIG. 3A,which has been eccentrically extruded to provide added torsionalstiffness;

FIG. 4A is a side view of the distal region shown in FIG. 3A, in whichthe catheter tube is stiffer than the sheath, and in which the cathetertube has been rotated within the sheath and flipped over upon itself;

FIG. 4B is a side view of the distal region shown in FIG. 3A, in whichthe catheter tube is not as stiff as the sheath, and in which thecatheter tube has been rotated within the sheath to form an orthogonalbend in the loop;

FIG. 5 is a side view of an embodiment of the distal region shown inFIG. 3A, in which the size of the slot through which the loop extendscan be varied;

FIG. 6 is a side view of an embodiment of the distal region shown inFIG. 3A , in which a prestressed spline within the loop structure altersthe geometry of the structure;

FIGS. 7A, 7B, and 7C are top views of different embodiments of thedistal region shown in FIG. 3A, in which the slot is shown havingdifferent geometries, which affect the geometry of the resulting loop;

FIG. 8 is a side view of an embodiment of the distal region shown inFIG. 3A, in which the proximal end of the slot is tapered to facilitateformation of the loop;

FIG. 9 is a side view of an embodiment of the distal region shown inFIG. 3A, in which the slot has a helical geometry;

FIG. 10 is a side view of the distal region shown in FIG. 9, with theloop support structure deployed through the helical slot;

FIG. 11 is a side view of an embodiment of the distal region shown inFIG. 3A, with the catheter tube having a prebent geometry orthogonal tothe loop structure;

FIG. 12 is a side view of an embodiment of the distal region shown inFIG. 11, with the sheath advanced forward to straighten the prebentgeometry;

FIG. 13A is a section view of the catheter tube within the sheath, inwhich the geometries of the sheath and catheter tube are extruded toprevent relative rotation;

FIG. 13B is a section view of the catheter tube within the sheath, inwhich the geometries of the sheath and catheter tube are extruded topermit limited relative rotation;

FIG. 14 is an enlarged side view of an alternative embodiment the distalregion of the probe shown in FIG. 1;

FIG. 15A is a side view of the distal region shown in FIG. 14, showingthe multiple electrode structure advanced from the associated sheath toform a loop;

FIG. 15B is a side view of an alternative embodiment of the distalregion shown in FIG. 14;

FIGS. 16A, 16B, and 16C are view of the distal region shown in FIG. 14,showing alternative ways to stiffen the flexible junction between thesheath and the catheter tube;

FIG. 17A is an enlarged side view of an alternative embodiment thedistal region of the probe shown in FIG. 1;

FIG. 17B is a section view of an embodiment of the distal region shownin FIG. 17A;

FIGS. 18, 19, and 20, are side sectional view, largely diagrammatic,showing an embodiment of the distal region shown in FIG. 1, in which theelectrode array is movable;

FIG. 21 is an enlarged side view of an alternative embodiment of thedistal region of the probe shown in FIG. 1, with the associated sheathwithdrawn and with no rearward force applied to the associated pullwire;

FIG. 22 is an enlarged side view of the distal region of the probe shownin FIG. 21, with the associated sheath advanced;

FIG. 23 is an enlarged side view of distal region of the probe shown inFIG. 21, with the associated sheath withdrawn and with rearward forceapplied to the associated pull wire to form a loop structure;

FIG. 24 is an enlarged side view of an alternative embodiment of thedistal region shown in FIG. 21, with a pivot connection;

FIG. 25 is an enlarged elevation side view of an alternative embodimentof the distal region of the probe shown in FIG. 1, showing a preformedloop structure;

FIG. 26 is an enlarged, side section view of the slidable end cap shownin FIG. 25;

FIG. 27 is a side view of the distal region shown in FIG. 25, with theinterior wire pulled axially to change the geometry of the preformedloop structure;

FIG. 28 is a side view of the distal region shown in FIG. 25, with theinterior wire bend across its axis to change the geometry of thepreformed loop structure;

FIG. 29 is a side view of the distal region shown in FIG. 25, with theinterior wire rotated about its axis to change the geometry of thepreformed loop structure;

FIGS. 30 and 31 are side views of the distal region shown in FIG. 25,with the location of the slidable cap moved to change the geometry ofthe preformed loop structure;

FIG. 32 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed, multiple spline loop structure;

FIG. 33 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 32, showing apreformed, multiple spline loop structure with asymmetric mechanicalstiffness properties;

FIG. 34 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed, multiple independent spline loop structures;

FIG. 35 is an enlarged elevation side view of an alternative embodimentof the distal region of the probe shown in FIG. 1, showing a preformedloop structure, which, upon rotation, forms an orthogonal bend;

FIG. 36 is an enlarged side view of the distal region shown in FIG. 35,with the orthogonal bend formed;

FIG. 37 is a section view of the distal region shown in FIG. 35, takengenerally along line 37—37 in FIG. 35;

FIG. 38 is a section view of the distal region shown in FIG. 35, takengenerally along line 38—38 in FIG. 35;

FIG. 39 is a section view of the distal region shown in FIG. 36, takengenerally along line 39—39 in FIG. 36;

FIG. 40 is an enlarged, perspective side view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apretwisted loop structure, which forms an orthogonal bend;

FIG. 41 is a side section view of a portion of the loop structure shownin FIG. 40, taken generally along line 41—41 in FIG. 40;

FIG. 42A is an enlarged side view of an alternative embodiment of thedistal region of the probe shown in FIG. 1, showing a preformed loopstructure, which, upon rotation, forms an orthogonal bend;

FIG. 42B is an enlarged side view of the distal region shown in FIG.42A, with the orthogonal bend formed;

FIG. 43 is an enlarged side perspective view of an alternativeembodiment of the distal region of the probe shown in FIG. 1, showing apreformed loop structure, which has a prestressed interior splineforming an orthogonal bend;

FIG. 44 is a largely diagrammatic view of the deployment of the distalregion of the probe shown in FIG. 1 in the right atrium of a heart;

FIG. 45 is a side elevation view of an alternative embodiment of thedistal region of the probe shown in FIG. 1, showing a self-anchoring,multiple electrode structure;

FIG. 46 is a section view of the self-anchoring structure shown in FIG.45;

FIG. 47 is a side elevation view of an embodiment of the distal regionshown in FIG. 45; in which the anchoring branch is movable;

FIG. 48 is a side elevation view of the distal region of the probe shownin FIG. 45, with the self-anchoring, multiple electrode structurewithdrawn within an associated sheath;

FIGS. 49A, 49B, and 49C show the deployment of the multiple,self-anchoring electrode structure shown in FIG. 45 within a bodyregion;

FIGS. 50A and 50B show, in diagrammatic form, the location of regionswithin the heart in which the self-anchoring structure shown in FIG. 45can be anchored;

FIG. 51 is a side view of an embodiment of the self-anchoring structureshown in FIG. 45, in which the branch carrying electrode elements can beadvanced or retracted or rotated along or about its axis;

FIG. 52 is a side view of an embodiment of the self-anchoring structureshown in FIG. 45, in which the branch carrying electrode elements can betorqued about the main axis of the structure;

FIG. 53 is a side elevation view of an alternative embodiment of thedistal region of the probe shown in FIG. 1, showing a self-anchoring,loop structure;

FIG. 54 is a side elevation view of an alternative embodiment of thedistal region shown in FIG. 53; also showing a type of a self-anchoring,loop structure;

FIG. 55 is a side elevation view of an alternative embodiment of thedistal region shown in FIG. 45, showing a self-anchoring structure withan active anchoring element;

FIG. 56 is a side view of an alternative embodiment of the distal regionof the probe shown in FIG. 1, showing a spanning branch structure;

FIG. 57 is a side sectional view of the spanning branch structure shownin FIG. 56, with the associated sheath advanced;

FIG. 58 is a side view of the spanning branch structure shown in FIG.56, with the associated sheath retracted and the structure deployed incontact with tissue;

FIG. 59 is a side view of an alternative embodiment a spanning branchstructure of the type shown in FIG. 56;

FIG. 60 is a side view of the spanning branch structure shown in FIG. 59deployed in contact with tissue;

FIG. 61 is a side view of an alternative embodiment of the distal regionof the probe shown in FIG. 1, showing a spring-assisted, spanning branchstructure;

FIG. 62 is a side sectional view of the spring-assisted, spanning branchstructure shown in FIG. 61, with the associated sheath advanced;

FIGS. 63A and 63B are side views of the deployment in a body region ofthe spring-assisted, spanning branch structure shown in FIG. 61;

FIG. 63C is a side view a spring-assisted, spanning branch structure,like that shown in FIG. 61, with an active tissue anchoring element;

FIG. 64 is a representative top view of long, continuous lesion patternin tissue;

FIG. 65 is a representative top view of segmented lesion pattern intissue;

FIG. 66 is a side view of an alternative embodiment of a self-anchoring,loop structure, showing the catheter tube detached from the associatedsheath;

FIG. 67 is a side view of the self-anchoring, loop structure shown inFIG. 66, with the catheter tube attached to the associated sheath;

FIG. 68 is a side view of the self-anchoring, loop structure shown inFIG. 67, showing the catheter tube advanced in an outwardly bowed loopshape from the associated sheath;

FIG. 69 is a side section view of a portion of the distal region shownin FIG. 66, showing the inclusion of a bendable spring to steer theself-anchoring loop structure;

FIG. 70 is a side view of the self-anchoring, loop structure shown inFIG. 67, showing the structure deployed for use within a body cavity;

FIG. 71 is a side view, with parts broken away and in section, of analternative embodiment of the self-anchoring, loop structure shown inFIG. 67, with an interference fit releasably coupling the catheter tubeto the associated sheath;

FIG. 72 is a side view, with parts broken away and in section, of analternative embodiment of the self-anchoring, loop structure shown inFIG. 67, with a releasable snap-fit coupling the catheter tube to theassociated sheath;

FIG. 73 is a side view of an alternative embodiment of theself-anchoring, loop structure shown in FIG. 67, with a pivotingconnection releasably coupling the catheter tube to the associatedsheath;

FIG. 74 is a side view of a embodiment of a pivoting connection of thetype shown in FIG. 73, with the catheter tube released from theassociated sheath;

FIG. 75 is a side view, with parts broken away and in section, thepivoting connection shown in FIG. 74, with the catheter tube attached tothe associated sheath;

FIG. 76 is a side perspective view of the pivoting connection shown inFIG. 75, with the catheter tube pivoting with respect to the associatedsheath;

FIG. 77A is an exploded, perspective view of an alternative embodimentof a releasable pivoting connection of the type shown in FIG. 73, withthe catheter tube detached from the associated sheath;

FIG. 77B is an exploded, perspective view of the reverse side of thepivoting connection shown in FIG. 77A, with the catheter tube detachedfrom the associated sheath;

FIG. 77C is a top side view of the releasable pivoting connection shownin FIG. 77A, with the catheter tube attached to the associated sheath;

FIG. 77D is a top side view of the releasable pivoting connection shownin FIG. 77C, with the catheter tube attached to the associated sheathand pivoted with respect to the sheath;

FIG. 78A is an exploded, perspective view of an alternative embodimentof a releasable pivoting connection of the type shown in FIG. 73, withthe catheter tube detached from the associated sheath;

FIG. 78B is a top view of the releasable pivoting connection shown inFIG. 78A, with the catheter tube attached to the associated sheath;

FIG. 78C is a top side view of the releasable pivoting connection shownin FIG. 78B, with the catheter tube attached to the associated sheathand pivoted with respect to the sheath;

FIG. 79 shows, in diagrammatic form, sites for anchoring aself-anchoring structure within the left or right atria;

FIGS. 80A to 80D show representative lesion patterns in the left atrium,which rely, at least in part, upon anchoring a structure with respect toa pulmonary vein;

FIGS. 81A to 81C show representative lesion patterns in the rightatrium, which rely, at least in part, upon anchoring a structure withrespect to the superior vena cava, the inferior vena cava, or thecoronary sinus;

FIG. 82 shows a loop structure of the type shown in FIG. 3A, whichcarries a porous ablation element;

FIG. 83 is a side section view of the porous ablation element takengenerally along line 83—83 in FIG. 82;

FIG. 84 is a side section view of an alternative embodiment of theporous ablation element, showing segmented ablation regions, takengenerally along line 84—84 in FIG. 85;

FIG. 85 is an exterior side view of the segmented ablation regions shownin section in FIG. 84;

FIG. 86 is a side section view of an alternative embodiment of a porouselectrode element of the type shown in FIG. 82;

FIG. 87 is a side view of a probe, like that shown in FIG. 1, thatincludes indicia for marking the extent of movement of the catheter tuberelative to the associated sheath;

FIG. 88 is a side view of an alternative embodiment of a probe, of thetype shown in FIG. 1, showing indicia for marking the extent of movementof the catheter tube relative to the associated sheath;

FIG. 89 is a side sectional view of a catheter tube having a movablesteering assembly;

FIG. 90 is an elevated side view of a preformed loop structure having amovable steering mechanism as shown in FIG. 89;

FIG. 91 is a section view of the loop structure shown in FIG. 90, takengenerally alone line 91—91 in FIG. 90;

FIG. 92 is an elevated side view of using the movable steering mechanismshown in FIG. 89 to change the geometry of the loop structure shown inFIG. 90;

FIG. 93 is an elevated side view of using two movable steeringmechanisms, as shown in FIG. 89, to change the geometry of a loopstructure;

FIG. 94 is a side view of an alternate embodiment of the self-anchoringloop structure having a pivoting connection;

FIG. 95 is a perspective view of the embodiment shown in FIG. 94;

FIG. 96 is a perspective view of the embodiment shown in FIG. 94;

FIG. 97 is a perspective view of an alternate embodiment of theself-anchoring loop structure shown in FIGS. 94-96;

FIG. 98 is a perspective view of another alternate embodiment of theself-anchoring loop structure shown in FIGS. 94-96;

FIG. 99 is a perspective view of another alternate embodiment of theself-anchoring loop structure shown in FIGS. 94-96;

FIG. 100 is a side view showing an exemplary use of the embodiment shownin FIG. 99; and

FIG. 101 is a perspective view of another alternate embodiment of theself-anchoring loop structure shown in FIGS. 94-96.

The invention may be embodied in several forms without departing fromits spirit or essential characteristics. The scope of the invention isdefined in the appended claims, rather than in the specific descriptionpreceding them. All embodiments that fall within the meaning and rangeof equivalency of the claims are therefore intended to be embraced bythe claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This Specification discloses various multiple electrode structures inthe context of catheter-based cardiac ablation. That is because thestructures are well suited for use in the field of cardiac ablation.

Still, it should be appreciated that the disclosed structures areapplicable for use in other applications. For example, the variousaspects of the invention have application in procedures requiring accessto other regions of the body, such as, for example, the prostrate,brain, gall bladder, and uterus.

The structures are also adaptable for use with systems that are notnecessarily catheter-based. For example, the structures disclosed hereinmay be used in conjunction with hand held surgical devices (or“probes”). The distal end of a probe may be placed directly in contactwith the targeted tissue area by a physician during a surgicalprocedure, such as open heart surgery for mitral valve replacement.Here, access may be obtained by way of a thoracotomy, median stemotomy,or thoracostomy.

Probe devices in accordance with the present invention preferablyinclude a handle, a relatively short shaft, and one of the distalassemblies described hereafter in the catheter context. Preferably, thelength of the shaft is about 4 inches to about 18 inches. This isrelatively short in comparison to the portion of a catheter body that isinserted into the patient (typically from 23 to 55 inches in length) andthe additional body portion that remains outside the patient. The shaftis also relatively stiff. In other words, the shaft is either rigid,malleable, or somewhat flexible. A rigid shaft cannot be bent. Amalleable shaft is a shaft that can be readily bent by the physician toa desired shape, without springing back when released, so that it willremain in that shape during the surgical procedure. Thus, the stiffnessof a malleable shaft must be low enough to allow the shaft to be bent,but high enough to resist bending when the forces associated with asurgical procedure are applied to the shaft. A somewhat flexible shaftwill bend and spring back when released. However, the force required tobend the shaft must be substantial.

I. Flexible Loop Structures

A. Slotted Jointed Sheath

FIG. 1 shows a multiple electrode probe 10 that includes a structure 20carrying multiple electrode elements 28.

The probe 10 includes a flexible catheter tube 12 with a proximal end 14and a distal end 16. The proximal end 14 has an attached handle 18. Themultiple electrode structure 20 is attached to the distal end 16 of thecatheter tube 14 (see FIG. 2A).

The electrode elements 28 can serve different purposes. For example, theelectrode elements 28 can be used to sense electrical events in hearttissue. Alternatively, or in addition, the electrode elements 28 canserve to transmit electrical pulses to measure the impedance of hearttissue, to pace heart tissue, or to assess tissue contact. In theillustrated embodiment, the principal use of the electrode elements 28is to transmit electrical energy, and, more particularly,electromagnetic radio frequency energy, to ablate heart tissue.

The electrode elements 28 are electrically coupled to individual wires(not shown in FIG. 1, but which will be discussed in greater detaillater) to conduct ablating energy to them. The wires from the structure20 are passed in conventional fashion through a lumen in the cathetertube 12 and into the handle 18, where they are electrically coupled to aconnector 38 (see FIG. 1). The connector 38 plugs into a source of RFablation energy.

As FIG. 2A shows, the support structure 20 comprises a flexible splineleg 22 surrounded by a flexible, electrically nonconductive sleeve 32.The multiple electrodes 28 are carried by the sleeve 32.

The spline leg 22 is preferably made from resilient, inert wire, likeNickel Titanium (commercially available as Nitinol material) or 17-7stainless steel. However, resilient injection molded inert plastic canalso be used. Preferably, the spline leg 22 comprises a thin,rectilinear strip of resilient metal or plastic material. Still, othercross sectional configurations can be used.

The spline leg 22 can decrease in cross sectional area in a distaldirection, by varying, e.g., thickness or width or diameter (if round),to provide variable stiffness along its length. Variable stiffness canalso be imparted by composition changes in materials or by differentmaterial processing techniques.

As FIG. 2B shows, the stiffness of the support structure 20 can bedynamically varied on the fly by providing a tapered wire 544 slidablymovable within a lumen 548 in the structure 20. Movement of the taperedwire 544 (arrows 546 in FIG. 2B) adjusts the region of stiffness alongthe support structure 20 during use.

The sleeve 32 is made of, for example, a polymeric, electricallynonconductive material, like polyethylene or polyurethane or Pebax ®material (polyurethane and nylon). The signal wires for the electrodes28 preferably extend within the sleeve 32.

The electrode elements 28 can be assembled in various ways. They can,for example, comprise multiple, generally rigid electrode elementsarranged in a spaced apart, segmented relationship along the sleeve 32.The segmented electrodes can each comprise solid rings of conductivematerial, like platinum, which makes an interference fit about thesleeve 32. Alternatively, the electrode segments can comprise aconductive material, like platinum-iridium or gold, coated upon thesleeve 32 using conventional coating techniques or an ion beam assisteddeposition (IBAD) process.

Alternatively, the electrode elements 28 can comprise spaced apartlengths of closely wound, spiral coils wrapped about the sleeve 32 toform an array of generally flexible electrode elements 28. The coils aremade of electrically conducting material, like copper alloy, platinum,or stainless steel, or compositions such as drawn-filled tubing. Theelectrically conducting material of the coils can be further coated withplatinum-iridium or gold to improve its conduction properties andbiocompatibility.

The electrode elements 28 can also comprise porous materials, whichtransmit ablation energy through transport of an electrified ionicmedium. Representative embodiments of porous electrode elements 28 areshown in FIGS. 82 to 85, and will be described in greater detail later.

The electrode elements 28 can be operated in a uni-polar mode, in whichthe ablation energy emitted by the electrode elements 28 is returnedthrough an indifferent patch electrode 420 (see FIG. 44) externallyattached to the skin of the patient. Alternatively, the elements 28 canbe operated in a bipolar mode, in which ablation energy emitted by oneor more electrode element 28 is returned through an electrode element 28on the structure 20 (see FIG. 3A).

The diameter of the support structure 20 (including the electrodeelements 28, flexible sleeve 32, and the spline leg 22) can vary fromabout 2 French to about 10 French.

The support structure 20 must make and maintain intimate contact betweenthe electrode elements 28 and the endocardium. Furthermore, the supportstructure 20 must be capable of assuming a relatively low profile forsteering and introduction into the body.

To accomplish these objectives, the probe 10 includes a sheath 26carried by the catheter tube 12. The distal section 30 of the sheath 26extends about the multiple electrode structure 20 (see FIGS. 1 and 2A).The distal section 30 of the sheath 26 is joined to the end of themultiple electrode structure, e.g. by adhesive or thermal bonding.

In the embodiment shown in FIG. 1, the proximal section 34 of the sheath26 terminates short of the handle 18 and includes a raised grippingsurface 36. The proximal section 34 also includes a hemostatic valve andside port (not shown) for fluid infusion. Preferably the hemostaticvalve locks about the catheter tube 12.

The distal section 30 of the sheath 26 (proximal of its connection tothe multiple electrode structure 20) includes a preformed slot 40, whichextends along the axis of the catheter tube 12 (see FIG. 2A). A portionof the multiple electrode structure 20 is exposed through the slot 40.

The length and size of the slot 40 can vary, as will be described ingreater detail later. The circumferential distance that slot 40 extendsabout the axis 42 can also vary, but is always less than the outerdiameter of the sheath 26. Thus, a remnant 44 of the sheath 26 underliesthe slot 40. In the illustrated embodiment, the slot 40 extends about180° about the sheath 26.

The catheter tube 12 is slidable within the sheath in a forward andrearward direction, as indicated by arrows 46 and 48 in FIG. 1. Bygrasping the raised gripping surface 36 at the proximal end of thesheath 26, and pushing the catheter tube 12 in the forward direction(arrow 46) through the sheath 26 (see FIG. 3A), the structure 20,secured to the catheter tube 12 and to the end 30 of the sheath 26,bends outwardly from the slot 40. The sheath remnant 44 forms a flexiblejoint, keeping the distal end of the structure 20 close to the cathetertube axis 42, while the element 20 bends into a loop, as FIG. 3A shows.The flexible joint 44 maintains loop stress within the structure 20, tothereby establish and maintain intimate contact between the electrodeelements 28 and tissue.

The physician can alter the diameter of the loop structure 20 from largeto small, by incrementally moving the catheter tube 12 in the forwardand rearward directions (arrows 46 and 48) through the sheath 26. Inthis way, the physician can manipulate the loop structure 20 to achievethe desired degree of contact between tissue and the electrode elements28.

If desired, the physician can, while grasping the raised grippingsurface 36, rotate the catheter tube 12 within the sheath 26. As FIG. 4Ashows, when the catheter tube 12 is torsionally stiffer than the sheath26, the relative rotation (arrow 50) flips the loop structure 20 overupon itself (compare FIGS. 3A and 4A), to place the electrode elements28 in a different orientation for tissue contact. As FIG. 4B shows, whenthe sheath 26 is torsionally stiffer than the catheter tube 12, rotationof the catheter tube within the sheath 26 bends the structure 20generally orthogonally to the axis of the loop.

By grasping the raised gripping surface 36 and pulling the catheter tube12 in the rearward direction (arrow 48), the physician draws themultiple electrode structure 20 back into the sheath 26, as FIG. 2Ashows. Housed within the sheath 26, the multiple electrode structure 20and sheath 26 form a generally straight, low profile geometry forintroduction into and out of a targeted body region.

The sheath 26 is made from a material having a greater inherentstiffness (i.e., greater durometer) than the support structure 20itself. Preferably, the sheath material is relatively thin (e.g., with awall thickness of about 0.005 inch) so as not to significantly increasethe overall diameter of the distal region of the probe 10 itself. Theselected material for the sheath 26 is preferably also lubricious, toreduce friction during relative movement of the catheter tube 12 withinthe sheath 26. For example, materials made from polytetrafluoroethylene(PTFE) can be used for the sheath 26.

Additional stiffness can be imparted by lining the sheath 26 with abraided material coated with, Pebax® material (comprising polyurethaneand nylon). Increasing the sheath stiffness imparts a more pronouncedD-shape geometry to the formed loop structure 20 orthogonal to the axisof the slot 40. Other compositions made from PTFE braided with a stiffouter layer and other lubricious materials can be used. Steps are takento keep remnants of braided materials away from the exposed edges of theslot 40. For example, the pattern of braid can be straightened to runessentially parallel to the axis of the sheath 26 in the region of theslot 40, so that cutting the slot does not cut across the pattern of thebraid.

The flexible joint 44 is durable and helps to shape the loop structure.The flexible joint 44 also provides an anchor point for the distal end16 of the catheter tube 12. The joint 44 also provides relatively largesurface area, to minimize tissue trauma. The geometry of the loopstructure 20 can be altered by varying either the stiffness or thelength of the flexible joint 44, or both at the same time.

As FIG. 3A shows, a stiffening element 52 can be placed along the joint44. For example, the stiffening element 52 can comprise an increaseddurometer material (e.g., from about 35 D to about 72 D), which isthermally or chemically bonded to the interior of the joint 44. Examplesof increased durometer materials, which will increase joint stiffness,include nylon, tubing materials having metal or nonmetallic braid in thewall, and Pebax® material. Alternatively, the stiffening element 52 cancomprise memory wire bonded to the interior of the joint 44. The memorywire can possess variable thickness, increasing in the proximaldirection, to impart variable stiffness to the joint 44, likewiseincreasing stiffness in the proximal direction. The memory wire can alsobe preformed with resilient memory, to normally bias the joint 44 in adirection at an angle to the axis of the slot 40.

As FIG. 3B shows, the stiffening element 52 can comprise one or morelumens 546 within the joint 44, which carry wire material 548. Thelumens 546 and wire material 548 can extend only in the region of thejoint 44, or extend further in a proximal direction into the main bodyof the sheath 26, to thereby impart greater stiffness to the sheath 26as well.

As FIG. 3C shows, greater stiffness for the joint 44 can be imparted byextruding the sheath 26 to possess an eccentric wall thickness. In thisarrangement, the wall of the sheath 26 has a region 550 of greaterthickness in the underbody of the sheath 26, which becomes the joint 44,than the region 552 which is cut away to form the slot 40. As shown inphantom lines in FIG. 3C, one or more of the lumens 546 can be extrudedin the thicker region 550, to receive wire material to further stiffenthe region of the joint 44.

Regardless of its particular form, the stiffening element 52 for thejoint 44 changes the geometry of the formed loop structure 20.

The geometry of the formed loop structure 20 can also be modified byaltering the shape and size of the slot 40. The slot periphery can havedifferent geometries, e.g., rectangular (see FIG. 7A), elliptical (seeFIG. 7B), or tapered (see FIG. 7C), to establish different geometriesand loop stresses in the formed structure 20.

The effective axial length of the slot 44 can be adjusted by use of amovable mandrel 54, controlled by a push-pull stylet member 56 (see FIG.5) attached to a slider controller 58 in the handle 18. Axial movementof the mandrel 54 affected by the stylet member 56 enlarges or decreasesthe effective axial length of the slot 44. A nominal slot length in therange of 1¼ inch to 1½ inch will provide the D-shape loop structure 20shown in FIG. 3A. Shorter slot lengths will provide a less pronouncedD-shape, with a smaller radius of curvature. Larger slot lengths willprovide a more pronounced D-shape, with a larger radius of curvature. AsFIG. 8 shows, the proximal edge 60 of the slot 40 can be tapereddistally to guide bending of the structure 20 into the desired loopshape while being advanced through the slot 40.

Instead of extending generally parallel to the catheter tube axis 42, asFIGS. 1 to 8 show, the slot 40 can extend across the catheter tube axis42, as FIG. 9 shows. When advanced from the cross-axis slot 40, the loopstructure 20 extends more orthogonally to the catheter tube axis 42, asFIG. 10 shows, compared to the more distal extension achieved when theslot 40 is axially aligned with the catheter tube axis 42, as FIG. 3Agenerally shows.

As FIG. 6 shows, a region 62 of the spline 22 within the structure 20away from the electrode elements 28 can be preformed with elastic memoryto bow radially away from the electrode elements 28 when advanced fromthe sheath 26. The radially outward bow of the preformed region 62 formsa more symmetric loop structure 20′, in contrast to the more asymmetricD-shaped loop 20 shown in FIG. 3A. When in contact with tissue, thepreformed, outwardly bowed region 62 generates a back pressure that, incombination with the loop stress maintained by the flexible joint 44,establishes greater contact pressure between electrode elements 28 andtissue.

In FIG. 6, the region 62 is preformed with a generally uniform bend in asingle plane. The region 62 can be preformed with complex, serpentinebends along a single plane, or with bends that extend in multipleplanes. Further details of representative loop structures havingcomplex, curvilinear geometries will be described in greater detaillater.

Additional tissue contact forces can be generated by mounting a bendablespring 64 in the distal end 16 of the catheter tube (see FIG. 2A). Oneor more steering wires 66 are bonded (e.g., soldered, spot welded, etc.)to the bendable spring 64 extend back to a steering mechanism 68 in thehandle 18 (see FIG. 1). Details of steering mechanisms that can be usedfor this purpose are shown in Lundquist and Thompson U.S. Pat. No.5,254,088, which is incorporated into this Specification by reference.Operation of the steering mechanism 68 pulls on the steering wires 66 toapply bending forces to the spring 64. Bending of the spring 64 bendsthe distal end 16 of the catheter tube 12, as shown in phantom lines inFIG. 1.

The plane of bending depends upon the cross section of the spring 64 andthe attachment points of the wires 66. If the spring 64 is generallycylindrical in cross section, bending in different planes is possible.If the spring 64 is generally rectilinear in cross section, anisotropicbending occurs perpendicular to the top and bottom surfaces of thespring 64, but not perpendicular to the side surfaces of the spring 64.

Alternatively, or in combination with the manually bendable spring 64,the distal end 16 of the catheter tube 12 can be prebent to form anelbow 70 (see FIG. 11) generally orthogonal or at some other selectedangle to the loop structure 20. In the illustrated embodiment, apreformed wire 72 is secured, e.g., by soldering, spot welding, or withadhesive, to the end 16 of the catheter tube 12. The preformed wire 72is biased to normally curve. The preformed wire 72 may be made fromstainless steel 17/7, nickel titanium, or other memory elastic material.It may be configured as a wire or as a tube with circular, elliptical,or other cross-sectional geometry.

The wire 72 normally imparts its curve to the distal catheter tube end16, thereby normally bending the end 16 in the direction of the curve.The direction of the normal bend can vary, according to the functionalcharacteristics desired. In this arrangement, a sheath 74 slides (arrows76) along the exterior of the catheter body 14 between a forwardposition overlying the wire 72 (FIG. 12) and an aft position away fromthe wire 72 (FIG. 11). In its forward position, the sheath 74 retainsthe distal catheter end 16 in a straightened configuration against thenormal bias of the wire 72, as FIG. 12 shows. The sheath 74 may includespirally or helically wound fibers to provide enhanced torsionalstiffness to the sheath 74. Upon movement of the sheath 74 to its aftposition, as FIG. 11 shows, the distal catheter end 16 yields to thewire 72 and assumes its normally biased bent position. The slidablesheath 74 carries a suitable gripping surface (not shown), like thegripping surface 36 of the sheath 26, to affect forward and aft movementof the sheath 74 for the purposes described.

FIG. 4 shows the loop structure 20 flipped upon itself by rotation ofthe loop structure 20 within the sheath 26. The rotation is allowed,because both the loop structure 20 and sheath 26 possess generallycylindrical cross sections. If it is desired to prevent relativerotation of the structure 20 within the sheath 26, the outer geometry ofthe structure 20 and the interior geometry of the sheath 26 can beformed as an ellipse, as FIG. 13A shows. The interference (ellipticallykeyed) arrangement in FIG. 13A prevents rotation of the structure 20 andalso provides improved torque response and maintains the electrodeelements 28 is a fixed orientation with respect to the sheath 26. Bymatching the outer geometry of the structure 20 and the interiorgeometry of the sheath 26 (see FIG. 13B), a prescribed range of relativerotation can be allowed before interference occurs. In FIG. 13B, theelliptical sleeve 32 will rotate until it contacts the butterfly shapedkeyway within the sheath 26. The prescribed range allows the loopstructure 20 to be flipped over upon itself in the manner shown in FIG.4, without wrapping the flexible joint 44 about the sheath 26. Shouldthe flexible joint 44 become wrapped about the sheath 26, the physicianmust rotate of the catheter tube 12 to unwrap the joint 44, beforeretracting the structure 20 back into the slotted sheath 26.

B. Distal Wire Joint

FIGS. 14 and 15 show another structure 100 carrying multiple electrodeelements 28. In many respects, the structure 100 shares structuralelements common to the structure 20 shown in FIGS. 2 and 3, as justdiscussed. For this reason, common reference numerals are assigned. Likethe structure 20 shown in FIGS. 2 and 3, the structure 100 is intended,in use, to be carried at the distal end 16 of a flexible catheter tube12, as a part of a probe 10, as shown in FIG. 1.

Like the structure 20 shown in the FIGS. 2 and 3, the support structure100 comprises a flexible spline leg 22 surrounded by a flexible,electrically nonconductive sleeve 32. The multiple electrodes 28 arecarried by the sleeve 32. The range of materials usable for the splineleg 22 and the electrodes 28 of the structure 100 are as previouslydescribed for the structure 20.

A sheath 102 is carried by the catheter tube 12. The distal section 104of the sheath 102 extends about the multiple electrode structure 100. AsFIGS. 14 and 15A show, the distal section 104 of the sheath 102 isjoined to the distal end 108 of the multiple electrode structure 100 bya short length of wire 106. The wire 106 is joined to the two ends 104and 108, for example, by adhesive or thermal bonding. The proximalsection of the sheath 102 is not shown in FIG. 13, but terminates shortof the handle 18 and includes a raised gripping surface 36, as shown forthe probe 10 in FIG. 1. In FIG. 15A, the wire 106 is joined to theinterior of the sheath 102. Alternatively, as FIG. 15B shows, the wire106 can be joined to the exterior of the sheath 102.

Like the sheath 26 described in connection with FIGS. 2 and 3A, thesheath 102 is made from a material having a greater inherent stiffnessthan the support structure 100 itself, e.g., composite materials madefrom PTFE, braid, and polyimide. The selected material for the sheath102 is preferably also lubricious. For example, materials made frompolytetrafluoroethylene (PTFE) can be used for the sheath 102. As forthe sheath 26 in FIGS. 2 and 3, additional stiffness-can be imparted byincorporating a braided material coated with Pebax® material.

The wire 106 comprises a flexible, inert cable constructed from strandsof metal wire material, like Nickel Titanium or 17-7 stainless steel.Alternatively, the wire 106 can comprise a flexible, inert stranded ormolded plastic material. The wire 106 in FIG. 14 is shown to be round incross section, although other cross sectional configurations can beused. The wire 106 may be attached to the sheath 102 by thermal orchemical bonding, or be a continuation of the spline leg 22 that formsthe core of the structure 100. The wire 106 can also extend through thewall of the sheath 102, in the same way that the stiffening wires 548are placed within the sheath 26 (shown in FIG. 3B). The need to providean additional distal hub component to secure the wire 106 to theremainder of the structure 100, is thereby eliminated.

The catheter tube 12 is slidable within the sheath 102 to deploy thestructure 100. Grasping the raised gripping surface 36 at the proximalend of the sheath 102, while pushing the catheter tube 12 in the forwarddirection through the sheath 102 (as shown by arrow 110 in FIG. 15A),moves the structure 100 outward from the open distal end 112 of thesheath 102. The wire 106 forms a flexible joint 143, pulling the distalend 108 of the structure 100 toward the sheath distal section 104. Thestructure 100 thereby is bent into a loop, as FIG. 15A shows.

The flexible wire joint 143, like the sheath joint 44 in FIG. 3A,possesses the flexibility and strength to maintain loop stress withinthe structure 100 during manipulation, to thereby establish and maintainintimate contact between the electrode elements 28 and tissue. The wire106 presents a relatively short length, thereby minimizing tissuetrauma. A representative length for the wire 106 is about 0.5 inch.

Like the loop structure 20, the physician can alter the diameter of theloop structure 100 from large to small, by incrementally moving thecatheter tube 12 in the forward direction (arrow 110 in FIG. 15) andrearward direction (arrow 116 in FIG. 15) through the sheath 102. Inthis way, the physician can manipulate the loop structure 100 to achievethe desired degree of contact between tissue and the electrode elements28.

Moving the structure 100 fully in the rearward direction (arrow 116)returns the structure 100 into a low profile, generally straightenedconfiguration within the sheath 102 (as FIG. 14 shows), well suited forintroduction into the intended body region.

The points of attachment of the wire joint 106 (between the distalstructure end 108 and the distal sheath section 104), coupled with itsflexible strength, make it possible to form loops with smaller radii ofcurvature than with the flexible sheath joint 44 shown in FIG. 3A.

The geometry of the loop structure 100 can be altered by varying eitherthe stiffness or the length of the flexible wire 106, or both at thesame time. As FIG. 16A shows, the flexible wire 106 can be tapered, toprovide a cross section that decreases in the distal direction. Thetapered cross section provides varying stiffness, which is greatest nextto the sheath 102 and decreases with proximity to the distal end 108 ofthe structure 100.

The stiffness can also be changed by changing the thickness of the wire106 in a step fashion. FIG. 16B shows the wire 106 attached to thesheath 102 and having the smallest thickness to increase the bendingradius. The thickness of the wire 106 increases in a step fashionleading up to its junction with the spline leg 22. Changing thethickness of the wire can be done by rolling the wire in steps, or bypressing it, or by chemical etching.

As FIG. 16C shows, the wire 106 can also be used to impart greaterstiffness to the flexible joint 143, for the reasons described earlierwith regard to the flexible joint 44 shown in FIG. 3A. In FIG. 16C, thewire 106 is thermally or chemically bonded to the flexible joint 143 ina serpentine path of increasing width. The alternative ways ofstiffening the flexible joint 44 (shown in FIGS. 3A, 3B, and 3C) canalso be used to stiffen the flexible joint 143.

In the illustrated embodiment (see FIGS. 15A and 16A), the distal sheathsection 104 is cut at an angle and tapered in a transverse directionrelative to the axis of the sheath 102. The angled linear cut on thedistal sheath section 104 may also be a contoured elongated opening (seeFIG. 15B) to make the initiation of the loop formation easier. The anglecut on the sheath 102 helps deploy and minimizes the length of the wire106. It is advantageous to cover with the sheath section 104 asignificant portion of the wire joint 143. The sheath section 104thereby also serves to shield the wire as much as possible from directsurface contact with tissue. The possibility of cutting tissue due tocontact with the wire 106 is thereby minimized.

As before described in the context of the structure 20, additionaltissue contact forces between the structure 100 and tissue can begenerated by mounting a bendable spring 64 in the distal end 16 of thecatheter tube (see FIG. 14). Alternatively, or in combination with themanually bendable spring 64, the distal end 16 of the catheter tube 12can be prebent to form an elbow 70 (as shown in FIG. 11 in associationwith the structure 20) generally orthogonal or at some other selectedangle to the loop structure 100.

FIG. 17A shows an alternative embodiment for the structure 100. In thisembodiment, the wire 106 is not attached to the distal sheath section104. Instead, the wire 106 extends through the sheath 102 to a stop 118located proximal to the gripping surface 36 of the sheath 102. Holdingthe stop 118 stationary, the physician deploys the loop structure 100 inthe manner already described, by advancing the catheter tube 12 throughthe sheath 102 (arrow 120 in FIG. 17A). Once the loop structure 100 hasbeen formed, the physician can pull on the wire 106 (arrow 122 in FIG.17A) to decrease its exposed length beyond the distal sheath section104, to minimize tissue trauma. Further adjustments to the loop are madeby advancing or retracting the catheter tube 12 within the sheath 102.The wire 106 unattached to the sheath 102 allows the physician tointerchangeably use the structure 100 with any sheath.

Alternatively, as FIG. 17B shows, the sheath 102 can include a lumen 107through which the wire 106 passes. In this embodiment, the presence ofthe wire 106 within the body of the sheath 102 provides increasedtorque. Unlike FIG. 17A, however, the sheath and the wire 106 compriseone integrated unit and cannot be interchanged.

The embodiment shown in schematic form in FIGS. 18, 19, and 20 offersadditional options for adjusting the nature and extent of contactbetween the electrode elements 28 and tissue. As FIG. 18 shows, aflexible spline leg 124 extends from an external push-pull control 126through the catheter tube 12 and is looped back to a point of attachment128 within the catheter tube 12. A sheath 130, made of an electricallyinsulating material, is slidable along the spline leg 124, both withinand outside the catheter tube 12. The sheath 130 carries the electrodeelements 28. The proximal end of the sheath 130 is attached to a pushpull control 132 exposed outside the catheter tube 12.

By pushing both controls 126 and 132 simultaneously (arrows 134 in FIG.19), both the spline leg 124 and the sheath 130 are deployed beyond thedistal end 16 of the catheter tube 12. Together, the spline leg andsheath 130 form a loop structure 136 to present the electrode elements28 for contact with tissue, in much the same way that the structure 100and the structure 20, previously described, establish contact betweenthe electrode elements 28 and tissue.

In addition, by holding the spline leg control 126 stationary whilepushing or pulling the sheath control 132 (arrows 134 and 136 in FIG.20), the physician is able to slide the sheath 130, and thus theelectrode elements 28 themselves, along the spline leg 124 (as arrows138 and 140 in FIG. 20 show). The physician is thereby able toadjustably locate the region and extent of contact between tissue andthe electrode elements 28.

Furthermore, by holding the sheath control 132 stationary while pushingor pulling upon the spline leg control 126, the physician is able toadjust the length of the spline leg 124 exposed beyond the distal end 16of the catheter tube 12. The physician is thereby able to incrementallyadjust the radius of curvature in generally the same fashion previouslydescribed in the context of FIG. 17.

The arrangement in FIGS. 18, 19, and 20, thereby provides a wide rangeof adjustment options for establishing the desired degree of contactbetween tissue and the electrode elements 28 carried by the loopstructure 136.

By pulling both controls 126 and 128 simultaneously (arrows 142 in FIG.18), both the spline leg 124 and the sheath 130 are moved to a positionclose to or within the distal end 16 of the catheter tube 12 forintroduction into a body region.

C. Free Pull Wire

FIG. 21 shows a multiple electrode support structure 144 formed from aspline leg 146 covered with an electrically insulating sleeve 148. Theelectrode elements 28 are carried by the sleeve 148.

The structure 144 is carried at the distal end 16 of a catheter tube 12,and comprises the distal part of a probe 10, in the manner shown in FIG.1. In this respect, the structure 144 is like the structure 100,previously described, and the same materials as previously described canbe used in making the structure 144.

Unlike the previously described structure 100, a slidable sheath 150 isintended to be moved along the catheter tube 12 and structure 144between a forward position, covering the structure 144 for introductioninto a body region (shown in FIG. 22), and an aft, retracted position,exposing the structure 144 for use (shown in FIGS. 21 and 23). Thus,unlike the structure 100, which is deployed by advancement forwardbeyond a stationary sheath 102, the structure 144 is deployed by beingheld stationary while the associated sheath 150 is moved rearward.

A pull wire 152 extends from the distal end 154 of the structure 144. Inthe illustrated embodiment,. the pull wire 152 is an extension of thespline leg 146, thereby eliminating the need for an additional distalhub component to join the wire 152 to the distal structure end 154.

Unlike the structure 100, the pull wire 152 is not attached to thesheath 150. Instead, the catheter tube 12 includes an interior lumen156, which accommodates sliding passage of the pull wire 152. The pullwire 152 passes through the lumen 156 to an accessible push-pull control166, e.g., mounted on a handle 18 as shown in FIG. 1. When the structure144 is free of the rearwardly withdrawn sheath 150, the physician pullsback on the wire 152 (arrow 168 in FIG. 23) to bend the structure 144into a loop.

As FIGS. 21 and 23 show, the wire 152 may include a preformed region 158adjacent to the distal structure end 154, wound into one or more loops,forming a spring. The region 158 imparts a spring characteristic to thewire 152 when bending the structure 144 into a loop. The region 158mediates against extreme bending or buckling of the wire 152 duringformation of the loop structure 144. The region 158 thereby reduces thelikelihood of fatigue failure arising after numerous flex cycles.

FIG. 24 shows an alternative embodiment for the structure 144. In thisembodiment, the distal structure end 154 includes a slotted passage 160,which extends across the distal structure end 154. In FIG. 24, theslotted passage 160 extends transverse of the main axis 162 of thestructure 144. Alternatively, the slotted passage 160 could extend atother angles relative to the main axis 162.

Unlike the embodiment shown in FIGS. 21 to 23, the wire 152 in FIG. 24is not an extension of the spline leg 146 of the structure 144. Instead,the wire 152 comprises a separate element, which carries a ball 164 atits distal end. The ball 164 is engaged for sliding movement within theslotted passage 160. The ball 164 also allows rotation of the wire 152relative to the structure 144. The ball 164 and slotted passage 160 forma sliding joint, which, like the spring region 158 in FIGS. 21 to 23,reduces the likelihood of fatigue failure arising after numerous flexcycles.

As before described in the context of the structure 100, additionaltissue contact forces between the structure 144 and tissue can begenerated by mounting a bendable spring 64 in the distal end 16 of thecatheter tube (see FIG. 21). Alternatively, or in combination with themanually bendable spring 64, the distal end 16 of the catheter tube 12can be prebent to form an elbow (like elbow 70 shown in FIG. 11 inassociation with the structure 20) generally orthogonal or at some otherselected angle to the loop structure 144.

D. Preformed Loop Structures

1. Single Loops

FIG. 25 shows an adjustable, preformed loop structure 170. The structure170 is carried at the distal end 16 of a catheter tube 12, which isincorporated into a probe, as shown in FIG. 1.

The structure 170 includes a single, continuous, flexible spline element172 having two proximal ends 174 and 176. One proximal end 174 issecured to the distal catheter tube end 16. The other proximal end 176slidably passes through a lumen 178 in the catheter tube 12. Theproximal end 176 is attached to an accessible push-pull control 180,e.g., mounted in the handle 18 shown in FIG. 1. The flexible splineelement 172 is bent into a loop structure, which extends beyond thedistal end 16 of the catheter tube 12. The spline element 172 can bepreformed in a normally bowed condition to accentuate the loop shape.

The continuous spline element 172 can be formed from resilient, inertwire, like Nickel Titanium or 17-7 stainless steel, or from resilientinjection molded inert plastic, or from composites. In the illustratedembodiment, the spline element 172 comprises a thin, rectilinear stripof resilient metal, plastic material, or composite. Still, other crosssectional configurations can be used.

As before described in connection with other structures, a sleeve 182made of, for example, a polymeric, electrically nonconductive material,like polyethylene or polyurethane or Pebax® material is secured, e.g.,by heat shrinking, adhesives, or thermal bonding about the splineelement 172 in a region of the structure 170. The sleeve 182 carries oneor more electrode elements 28, which can be constructed in mannerspreviously described.

The structure 170 includes an interior wire 184. The interior wire canbe made from the same type of materials as the spline element 172. Thedistal end of the wire 184 carries a cap 186, which is secured, e.g., bycrimping or soldering or spot welding, to the wire 184. The cap includesa through passage 188 (see FIG. 26), through which the mid portion ofthe spline element 172 extends. The spline element 172 is slidablewithin the through passage 188. It should be appreciated that the wire184 can be attached to the spline element 172 in other ways to permitrelative movement, e.g., by forming a loop or eyelet on the distal endof the wire 184, through which the spline leg 172 passes. It should alsobe appreciated that the cap 186 can be secured to the spline leg 172, ifrelative movement is not desired.

The proximal end of the interior wire 184 slidably passes through alumen 190 in the catheter tube 12 for attachment to an accessiblepush-pull control 192, e.g., also on a handle 18 like that shown in FIG.1.

As FIG. 27 shows, pushing on the control 180 (arrow 194) or pulling onthe control 180 (arrow 196) moves the spline element 172 to alter theshape and loop stresses of the structure 170. Likewise, pushing on thecontrol 192 (arrow 198) or pulling on the control 192 (arrow 200) movesthe interior wire 184 in the lumen 190, which applies force to the cap186 in the midportion of the structure 172, and which further alters theshape and loop stresses of the structure 170.

In particular, manipulation of the controls 180 and 192 createsasymmetric geometries for the structure 170, so that the physician isable to shape the structure 170 to best conform to the interior contoursof the body region targeted for contact with the electrode elements.Manipulation of the controls 180 and 192 also changes the backpressures, which urge the electrode elements 28 into more intimatecontact with tissue.

As FIG. 28 shows, further variations in the shape of and physical forceswithin the structure 170 can be accomplished by bending the interiorwire 184 along its axis. In one embodiment, the wire 184 is made fromtemperature memory wire, which bends into a preestablished shape inresponse to exposure to blood (body) temperature, and which straightensin response to exposure to room temperature. Bending the interior wire184 imparts forces (through the cap 186) to bend the spline element 172into, for example, an orthogonal orientation. This orientation may berequired in certain circumstances to better access the body region wherethe electrode elements 28 are to be located in contact with tissue.

Alternatively, one or more steering wires (not shown) can be attached tothe interior wire 184. Coupled to an accessible control (not shown),e.g. on the handle 18, pulling on the steering wires bends the wire 184,in generally the same fashion that the steering wires 66 affect bendingof the spring 64, as previously described with reference to FIG. 2A.

As FIG. 29 shows, the control 192 can also be rotated (arrows 222) totwist the interior wire 184 about its axis. Twisting the wire 184imparts (through the cap 186) transverse bending forces along the splineelement 172. The transverse bending forces form curvilinear bends alongthe spline element 172, and therefore along the electrode elements 28 aswell. The loop stresses can also be further adjusted by causing thecontrol 180 to rotate (arrows 224) the spline element 172.

As FIG. 30 shows, the through passage cap 186 (see FIG. 26) permits thecap 186 to be repositioned along the spline element 172. In this way,the point where the wire 184 applies forces (either push-pull, ortwisting, or bending, or a combination thereof) can be adjusted toprovide a diverse variety of shapes (shown in phantom lines) for andloop stresses within the structure 170. FIG. 31 shows, by way ofexample, how changing the position of the cap 186 away from themidregion of the spline element 172 alters the orthogonal bend geometryof the spline element 172, compared to the bend geometry shown in FIG.28. The cap 186 can be moved along the spline element 172, for example,by connecting steering wires 566 and 568 to the distal region of theinterior wire 184. Pulling on a steering wire 566 or 568 will bend theinterior wire 184 and slide the cap 186 along the spline element 172.

The single loop structure 170 is introduced into the targeted bodyregion within an advanceable sheath 218, which is slidably carried aboutthe catheter tube 12 (see FIG. 25). Movement of the sheath 218 forward(arrow 226 in FIG. 25) encloses and collapses the loop structure 170within the sheath 218 (in generally the same fashion that the structure144 in FIG. 21 is enclosed within the associated sheath 150). Movementof the sheath 218 rearward (arrow 230 in FIG. 25) frees the loopstructure 170 of the sheath 218.

2. Multiple Loop Assemblies

As FIG. 32 shows, the structure 170 can include one or more auxiliaryspline elements 202 in regions of the structure 170 spaced away from theelectrode elements 28. In the illustrated embodiment, the auxiliaryspline elements 202 slidably extend through the distal cap 186 as beforedescribed, and are also coupled to accessible controls 204 in the mannerjust described. In this way, the shape and loop stresses of theauxiliary spline elements 202 can be adjusted in concert with the splineelement 172, to create further back pressures to urge the electrode 28toward intimate contact with tissue. The existence of one or moreauxiliary spline elements 202 in multiple planes also make it possibleto press against and expand a body cavity, as well as provide lateralstability for the structure 170.

As FIG. 33 shows, asymmetric mechanical properties can also be impartedto the structure 170, to improve contact between tissue and theelectrode elements 28. In FIG. 33, the region of the structure 170 whichcarries the electrode elements 28 is stiffened by the presence of theclosely spaced multiple spline elements 206A, 206B, and 206C. Spacedapart, single spline elements 208 provide a back-support region 210 ofthe structure 170.

FIG. 34 shows a multiple independent loop structure 220. The structure220 includes two or more independent spline elements (three splineelements 212, 214, and 216 are shown), which are not commonly joined bya distal cap. The spline elements 212, 214, and 216 form independent,nested loops, which extend beyond the distal end 16 of the catheter tube12.

A region 211 on each spline element 212, 214, and 216 carries theelectrode elements 28. The other region 213 of each spline element 212,214, and 216 is slidable within the catheter tube 12, being fitted withaccessible controls 212C, 214C, and 216C, in the manner just described.Thus, independent adjustment of the shape and loop stresses in eachspline element 212, 214, and 216 can be made, to achieve desired contactbetween tissue and the electrode elements 28.

Like the single loop structures shown in FIGS. 25 to 31, the variousmultiple loop structures shown in FIGS. 32 to 34 can be introduced intothe targeted body region in a collapsed condition within a sheath 232(see FIG. 32), which is slidably carried about the catheter tube 12. AsFIG. 32 shows, movement of the sheath 232 away from the loop structurefrees the loop structure for use.

E. Orthogonal Loop Structures

FIGS. 28 and 31 show embodiments of loop structures 170, which have beenbent orthogonally to the main axis of the structure 170. In theseembodiments, the orthogonal bending is in response to bending aninterior wire 184.

FIGS. 35 and 36 show a loop structure 232 that assumes an orthogonalgeometry (in FIG. 36) without requiring an interior wire 184. Thestructure 232, like the structure 170 shown in FIG. 25, is carried atthe distal end 16 of a catheter tube 12, which is incorporated into aprobe, as shown in FIG. 1.

Like the structure 170, the structure 232 comprises a single,continuous, flexible spline element 234. One proximal end 236 is securedto the distal catheter tube end 16. The other proximal end 238 passesthrough a lumen 240 in the catheter tube 12. The proximal end 238 isattached to an accessible control 242, e.g., mounted in the handle 18shown in FIG. 1. As in the structure 170, the spline element 234 can bepreformed in a normally bowed condition to achieve a desired loopgeometry.

In FIGS. 35 and 36, the spline element 234 is formed, e.g., from inertwire, like Nickel Titanium or 17-7 stainless steel, or from resilientinjection molded inert plastic, with two regions 244 and 246 havingdifferent cross section geometries. The region 244, which comprises theexposed part of the spline element 234 that carries the electrodeelements 28, possesses a generally rectilinear, or flattened crosssectional geometry, as FIG. 37 shows. The region 246, which comprisesthe part of the spline element 234 extending within the catheter tube 12and attached to the control 240, possesses a generally round crosssectional geometry, as FIG. 38 shows. To provide the two regions 244 and246, a single length of round wire can be flattened and annealed at oneend to form the rectilinear region 244.

Rotation of the control 242 (attached to the round region 246) (arrows250 in FIG. 35) twists the rectilinear region 244 about the proximal end236, which being fixed to the catheter tube 12, remains stationary. Thetwisting rectilinear region 244 will reach a transition position, inwhich the region 244 is twisted generally 90° from its original position(as FIG. 39 shows). In the transition position, the loop structure 232bends orthogonal to its main axis, as FIG. 36 shows. By stoppingrotation of the control 242 once the transition position is reached, theretained twist forces in the loop structure 232 hold the loop structure232 in the orthogonally bent geometry.

FIGS. 42A and 42B show an alternative embodiment, in which each leg 554and 556 of a loop structure 558 is attached to its own individualcontrol, respectively 560 and 562. The region 564 of the loop structure558 carrying the electrode element 28 possesses a generally rectilinearor flattened cross section. The regions of the legs 554 and 556 near thecontrols 560 and 562 possess generally round cross sections. Counterrotation of the controls 560 and 562 (respectively arrows 561 and 563 inFIG. 42B), twists the rectilinear region 564 to bend the loop structure558 generally orthogonal to its axis (as FIG. 42B shows). The counterrotation of the controls 560 and 562 can be accomplished individually orwith the inclusion of a gear mechanism.

In both embodiments shown in FIG. 36 and 42B, once the orthogonal bendis formed and placed into contact with tissue, controlled untwisting ofthe spline legs will begin to straighten the orthogonal bend in thedirection of tissue contact. Controlled untwisting can thereby be usedas a counter force, to increase tissue contact.

The characteristics of the orthogonally bent geometry depend upon thewidth and thickness of the rectilinear region 244. As the ratio betweenwidth and thickness in the region 244 increases, the more pronounced andstable the orthogonal deflection becomes.

The diameter of the loop structure 232 also affects the deflection. Thesmaller the diameter, the more pronounced the deflection. Increases indiameter dampen the deflection effect. Further increases beyond a givenmaximum loop diameter cause the orthogonal deflection effect to be lost.

The characteristics of the electrical insulation sleeve 248, whichcarries the electrode elements 28, also affect the deflection. Generallyspeaking, as the stiffness of the sleeve 248 increases, the difficultyof twisting the region 244 into the transition position increases. Ifthe sleeve 248 itself is formed with a non-round cross section, e.g.elliptical, in the rectilinear region 244 the orthogonal deflectioncharacteristics are improved.

The orthogonal deflection effect that FIGS. 35 and 36 show can also beincorporated into the loop structure of the type previously shown inFIG. 14. In this embodiment (see FIG. 40), the loop structure 252comprises a spline leg 254 (see FIG. 41 also) enclosed within anelectrically conductive sleeve 256, which carries the electrode elements28. The distal end of the structure 252 is attached by a joint wire 260to a sheath 258. As previously described, advancing the structure 252from the sheath 258 forms a loop (as FIG. 40 shows).

In the embodiment shown in FIG. 40, the spline leg 254 is rectilinear incross section (see FIG. 41). Furthermore, as FIG. 41 shows, the splineleg 254 is preformed in a normally twisted condition, having twosections 262 and 264. The section 262 is distal to the section 264 andis attached to the joint wire 260. The sections 262 and 264 are arrangedessentially orthogonally relative to each other, being offset by about900. When advanced outside the sheath 258, the twisted bias of therectilinear spline leg 254 causes the formed loop structure 252 to bendorthogonally to its main axis, as FIG. 40 shows.

In an alternative embodiment (see FIG. 43), the structure 252 caninclude a spline leg 266 preformed to include along its length one ormore stressed elbows 268. The prestressed elbows 268 impart anorthogonal deflection when the structure 252 is free of the constraintof the sheath 270. When housed within the sheath 270, the stiffness ofthe sheath 270 straightens the elbows 268.

F. Deployment of Flexible Loop Structures

1. Generally

Various access techniques can be used to introduce the previouslydescribed multiple electrode structures into a desired region of thebody. In the illustrated embodiment (see FIG. 44), the body region isthe heart, and the multiple electrode structure is generally designatedES.

During introduction, the structure ES is enclosed in a straightenedcondition within its associated outer sheath (generally designated S inFIG. 44) at the end 16 of the catheter tube 12. To enter the rightatrium of the heart, the physician directs the catheter tube 12 througha conventional vascular introducer (designated with a capital-I in FIG.44) into, e.g., the femoral vein. For entry into the left atrium, thephysician can direct the catheter tube 12 through a conventionalvascular introducer retrograde through the aortic and mitral valves, orcan use a transeptal approach from the right atrium.

Once the distal end 16 of the catheter tube 12 is located within theselected chamber, the physician deploys the structure ES in the mannerspreviously described, i.e., either by advancing the structure ES forwardthrough the sheath S (e.g., as in the case of the structures shown inFIGS. 3 or 15) or by pulling the sheath S rearward to expose thestructure ES (e.g., as in the case of the structures shown in FIGS. 21or 25).

It should be appreciated that the structure ES discussed above in thecontext of intracardiac use, can also be directly applied to theepicardium through conventional thoracotomy or thoracostomy techniques.

2. Loop Structures

The various loop structures previously described (shown in FIGS. 1 to31), when deployed in the left or right atrium tend to expand the atriumto its largest diameter in a single plane. The loop structure tends toseek the largest diameter and occupy it. The loop structures can also beadapted to be torqued, or rotated, into different planes, and therebyoccupy smaller regions.

The addition of auxiliary splines, such as shown in FIGS. 32 to 34serves to expand the atrium in additional planes. The auxiliary splinesalso make it possible to stabilize the structure against a more rigidanatomic structure, e.g. the mitral valve annulus in the left atrium,while the spline carrying the electrode elements loops upward towardanatomic landmarks marking potential ablation sites, e.g., tissuesurrounding the pulmonary veins.

The various structures heretofore described, which exhibit compound ororthogonal bends (see, e.g., FIGS. 28, 31, 35, 40, 42, and 43) (whichwill be referred to as a group as “Compound Bend Assemblies”) also makeit possible to locate the ablation and/or mapping electrode(s) at anylocation within a complex body cavity, like the heart. With priorconventional catheter designs, various awkward manipulation techniqueswere required to position the distal region, such as prolapsing thecatheter to form a loop within the atrium, or using anatomical barrierssuch as the atrial appendage or veins to support one end of the catheterwhile manipulating the other end, or torquing the catheter body. Whilethese techniques can still be used in association with the compound bendassemblies mentioned above, the compound bend assemblies significantlysimplify placing electrode(s) at the desired location and thereaftermaintaining intimate contact between the electrode(s) and the tissuesurface. The compound bend assemblies make it possible to obtain bettertissue contact and to access previously unobtainable sites, especiallywhen positioning multiple electrode arrays.

Compound bend assemblies which provide a proximal curved sectionorthogonal to the distal steering or loop geometry plane allow thephysician to access sites which are otherwise difficult and oftenimpossible to effectively access with conventional catheterconfigurations, even when using an anatomic barrier as a supportstructure. For example, to place electrodes between the tricuspidannulus and the cristae terminalis perpendicular to the inferior venacava and superior vena cava line, the distal tip of a conventional thecatheter must be lodged in the right ventricle while the catheter istorqued and looped to contact the anterior wall of the right atrium.Compound bend assemblies which can provide a proximal curved sectionorthogonal to the distal steering or loop geometry plane greatlysimplify positioning of electrodes in this orientation. Compound bendassemblies which provide a proximal curved section orthogonal to thedistal steering or loop geometry plane also maintain intimate contactwith tissue in this position, so that therapeutic lesions contiguous inthe subepicardial plane and extending the desired length, superiorlyand/or inferiorly oriented, can be accomplished to organize and helpcure atrial fibrillation.

A transeptal approach will most likely be used to create left atriallesions. In a transeptal approach, an introducing sheath is insertedinto the right atrium through the use of a dilator. Once thedilator/sheath combination is placed near the fossa ovalis underfluoroscopic guidance, a needle is inserted through the dilator and isadvanced through the fossa ovalis. Once the needle has been confirmed toreside in the left atrium by fluoroscopic observation of radiopaquecontrast material injected through the needle lumen, the dilator/sheathcombination is advanced over the needle and into the left atrium. Atthis point, the dilator is removed leaving the sheath in the leftatrium.

A left atrial lesion proposed to help cure atrial fibrillationoriginates on the roof of the left atrium, bisects the pulmonary veinsleft to right and extends posteriorly to the mitral annulus. Since thelesion described above is perpendicular to the transeptal sheath axis, acatheter which can place the distal steering or loop geometry planeperpendicular to the sheath axis and parallel to the axis of the desiredlesion greatly enhances the ability to accurately place the ablationand/or mapping element(s) and ensures intimate tissue contact with theelement(s). To create such lesions using conventional catheters requiresa retrograde procedure. The catheter is advanced through the femoralartery and aorta, past the aortic valve, into the left ventricle, upthrough the mitral valve, and into the left atrium. This approachorients the catheter up through the mitral valve. The catheter must thenbe torqued to orient the steering or loop geometry plane parallel to thestated lesion and its distal region must be looped over the roof of theleft atrium to position the ablation and/or mapping element(s) bisectingthe left and right pulmonary veins and extending to the mitral annulus.

Preformed guiding sheaths have also been employed to change cathetersteering planes. However, preformed guiding sheaths have been observedto straighten in use, making the resulting angle different than thedesired angle, depending on the stiffness of the catheter. Furthermore,a guiding sheath requires a larger puncture site for a separateintroducing sheath, if the guiding sheath is going to be continuouslyinserted and removed. Additional transeptal punctures increase thelikelihood for complications, such as pericardial effusion andtamponade.

G. Loop Size Marking

FIG. 87 shows a probe 524 comprising a catheter tube 526 carrying aslotted sheath 528 of the type previously described and shown, e.g., inFIG. 1. The catheter tube 526 includes proximal handle 529 and a distalmultiple electrode array 530. The multiple electrode array 530 isdeployed as a loop structure from the slotted sheath 528, in the mannerpreviously described and shown, e.g., in FIG. 3A.

In FIG. 87, the probe 524 includes indicia 532 providing the physicianfeedback on the size of the formed loop structure. In FIG. 87, theindicia 532 comprises markings 534 on the region of the catheter tube526 extending through the proximal end of the sheath 528. The markings534 indicate how much of the catheter tube 526 has been advanced throughthe sheath 528, which thereby indicates the size of the formed loopstructure.

The markings 534 can be made in various ways. They can, for example, beplaced on the catheter tube 526 by laser etching, or by printing on thecatheter tube 526 using bio-compatible ink, or by the attachment of oneor more premarked, heat shrink bands about the catheter tube 526.

In FIG. 88, the slotted sleeve 528 is attached to the handle 529 of theprobe 524. In this arrangement, the catheter tube 526 is advanced andretracted through the slotted sheath 528 by a push-pull control 536 onthe handle 529. In this embodiment, the indicia 532 providing feedbackas to the size of the formed loop structure includes markings 536 on thehandle 529, arranged along the path of travel of the push-pull control536. The markings 536 can be applied to the handle 529, e.g., by laseretching or printing. As in FIG. 87, the markings 536 indicate how muchof the catheter tube 526 has been advanced through the slotted sheath528.

H. Movable Steering

FIG. 89 shows a movable steering assembly 570. The assembly 570 includesa bendable wire 572 with at least one attached steering wire (two wires574 and 576 are shown). The steering wires 574 and 576 are attached,e.g. by spot welding or soldering, to the bendable wire 572. Thebendable wire 572 can be formed from resilient, inert wire, like NickelTitanium or 17-7 stainless steel, or from resilient injection moldedinert plastic, or from composites. In the illustrated embodiment, thewire 572 comprises a rectilinear strip of resilient metal, plasticmaterial, or composite. Still, other cross sectional configurations canbe used. The distal end 598 of the wire 572 is formed as a ball oranother blunt, nontraumatic shape.

The steering wires 574 and 576 are attached to an accessible control584. The control 584 can take the form, for example, of a rotatable camwheel mechanism of the type shown in Lundquist and Thompson U.S. Pat.No. 5,254,088, which is already incorporated into this Specification byreference. Pulling on the steering wires 574 and 576 (arrows 600 in FIG.89), e.g., by rotating the control 584, bends the wire 572 in thedirection of the pulling force.

The bendable wire 572 is attached by a ferrule 580 to a guide coil 578.The guide coil 578 provides longitudinal support for the bendable wire572. The guide coil 578 acts as the fulcrum about which the steeringassembly 570 bends.

The assembly 570, comprising the bendable wire 572, steering wires 574and 576, and guide coil 578, is carried within an outer flexible tube582. Operation of the control 584, to deflect the wire 572 within thetube 582, bends the tube 582.

Taking into account the rectilinear shape of the bendable wire 572, theouter tube 582 is ovalized. The interference between the rectilinearexterior shape of the wire 572 and the oval interior shape of the tube582 prevents rotation of the wire 572 within the tube 582. Theinterference thereby retains a desired orientation of the bendable wire572 with respect to the tube 582, and thus the orientation of theapplied bending forces.

The assembly 570 is attached to an accessible control 582. Pushing andpulling on the control 570 (arrows 602 and 604 in FIG. 89) axially movesthe steering assembly 570 within the tube 582. Axial movement of theassembly 570 changes the axial position of the bendable wire 572 withinthe tube 582. The control 570 thereby adjusts the location where bendingforces are applied by the wire 572 along the axis of the tube 582.

FIGS. 90 and 91 show the movable steering assembly 570 incorporated intoa loop structure 586 of the type previously disclosed with reference toFIG. 25, except there is no interior wire 184. The loop structure 586includes a spline 588 (see FIG. 91), which forms a loop. A sleeve 590surrounds the spline 588. One or more electrode elements 28 are carriedby the sleeve 590.

As FIG. 91 shows, the sleeve 590 includes an ovalized interior lumen592, which carries the movable steering assembly 570. The steeringassembly 570, attached to the accessible control 582, is movable withinthe lumen 592 along the spline 588, in the manner just described withrespect to the ovalized tube 582 in FIG. 89.

As FIG. 92 shows, operating the control 584 to actuate the steeringwires 574 and 576 exerts a bending force (arrow 604) upon the spline 588(through the bendable wire 572). The bending force alters the shape ofthe loop structure 586 in the plane of the loop, by increasing ordecreasing its diameter. Shaping the loop structure 586 using thesteering mechanism 570 adjusts the nature and extent of tissue contact.

Because the steering mechanism 570 is movable, the physician canselectively adjust the location of the bending force (arrow 604) to takeinto account the contour of the tissue in the particular accessed bodyregion.

As FIG. 93 shows, the loop structure 586 can carry more than one movablesteering mechanism. In FIG. 93, there are two moveable steeringmechanisms, designated 570(1) and 570(2), one carried on each leg of thestructure 586. A separate steering control designated 584(1) and 584(2),and a separate axial movement control, designated 582(1) and 582(2) canalso be provided. It is therefore possible to independently adjust theposition of each steering mechanism 570(1) and 570(2) and individuallyapply different bending forces, designated, respectively, arrows 604(1)and 604(2). The application of individually adjustable bending forces(arrows 604(1) and 604(2)) allow diverse changes to be made to the shapeof the loop structure 586.

It should also be appreciated that the movable steering mechanism 570can be incorporated into other loop structures including those of thetype shown in FIG. 33.

II. Self-Anchoring Multiple Electrode Structures

A. Integrated Branched Structures

FIGS. 45 and 46 show an integrated branched structure 272, whichcomprises an operative branch 274 and an anchoring branch 276 orientedin an angular relationship. The branched structure 274 occupies thedistal end 16 of a catheter tube 12, and forms the distal part of aprobe 10, as shown in FIG. 1.

It should be appreciated that there may be more than one operativebranch or more than one anchoring branch. The two branches 274 and 276are shown and described for the purpose of illustration.

The operative branch 274 carries one or more operative elements. Theoperative elements can take various forms. The operative elements can beused, e.g., to sense physiological conditions in and near tissue, or totransmit energy pulses to tissue for diagnostic or therapeutic purposes.As another example, the operative elements may take the form of one ormore tissue imaging devices, such as ultrasound transducers or opticalfiber elements. By way of further example, the operative elements cancomprise biopsy forceps or similar devices, which, in use, handletissue. The operative elements can also comprise optical fibers forlaser ablation, or a fluorescence spectroscopy device.

In the illustrated embodiment, the operative elements take the form ofthe electrode elements 28 (as previously described). In use, theelectrode elements 28 contact tissue to sense electrical events, or totransmit electrical pulses, e.g., to measure the impedance of or to paceheart tissue, or to transmit electrical energy to ablate tissue.

In the illustrated embodiment, the operative branch 274 comprises aspline element 282 enclosed within an electrically insulating sleeve284. The spline element 282 can be formed, e.g., from resilient, inertwire, like Nickel Titanium or 17-7 stainless steel, or from resilientinjection molded inert plastic. In the illustrated embodiment, thespline element 282 comprises a thin, rectilinear strip of resilientmetal or plastic material. Still, other cross sectional configurationscan be used. Furthermore, more than a single spline element may be used.

As before described in the context of other structures, a sleeve 284made of, for example, a polymeric, electrically nonconductive material,like polyethylene or polyurethane or Pebax® material is secured aboutthe spline element 282. The sleeve 284 carries the electrode elements28, which can also be constructed in manners previously described.

In the illustrated embodiment, the operative branch 274 extends at abouta 45° angle from the anchoring branch 276. Various other angles between0° (i.e., parallel) and 90° (i.e., perpendicular) can be used.

The angular relationship between the operative branches 274 and theanchoring branch 276 causes the operative branch 274 to inherently exertforce against tissue as it is advanced toward it. The spline element282, or the sleeve 284, or both, can be stiffened to bias the operativebranch 274 toward the anchoring branch 276, to thereby enhance theinherent tissue contact force.

As FIG. 46 best shows, the anchoring branch 276 comprises a tubular body286 defining an interior lumen 288, which extends through the cathetertube 12. The distal end 290 of the body 286 may be extended outwardbeyond the distal end 16 of the catheter tube 12, generally along thesame axis 292 as the catheter tube 12. The proximal end 296 of the body286 communicates with an accessible inlet 294, e.g., located on thecatheter tube 12 or on the handle 18.

The inlet 294 accommodates passage of a conventional guide wire 306 intoand through the lumen 288. The guide wire 306 includes a blunt distalend 308 for nontraumatic contact with tissue.

As FIG. 47 shows, the body 286 can be carried within the catheter tube12 for sliding movement forward (arrow 298) or rearward (arrow 300). Inthis embodiment, an accessible control 302, e.g., located on the handle18, is coupled to the body 286 to guide the movement. In this way, thephysician can withdraw the body 286 within the catheter tube 12 duringintroduction of the structure 272 into the body region. The physiciancan also adjust the relative length of the body 286 beyond the distalend 16 of the catheter tube 16 to aid in positioning and anchoring thestructure 272, once deployed within the targeted body region.

An exterior sheath 304 is slidable along the catheter tube 12 between aforward position (FIG. 48) and a rearward position (FIG. 45). In theforward position, the sheath 304 encloses and shields the operativebranch 274, straightening it. When in the forward position, the sheath304 also encloses and shields the anchoring branch 274. In the rearwardposition, the sheath 304 frees both branches 274 and 276 for use.

In use within the heart (see FIGS. 49A, 49B, and 49C), the physicianmaneuvers the guide wire 306 through and outwardly of the lumen 288,with the aid of fluoroscopy or imaging, to a desired anchor site. FIGS.50A and 50B show candidate anchor sites within the heart, which surroundanatomic structures that most commonly develop arrhythmia substrates,such as the superior vena cava SVC; right pulmonary veins (RPV); andleft pulmonary veins (LPV); inferior vena cava (IVC); left atrialappendage (LAA); right atrial appendage (RAA); tricuspid annulus (TA);mitral annulus (MA); and transeptal puncture (TP). The physicianpositions the blunt end portion 308 near tissue at the anchor site (seeFIG. 49A).

As FIG. 49B shows, the physician advances the structure 272, enclosedwithin the sheath 304, along the anchored guide wire 306. When near theanchor site, the physician retracts the sheath 304, freeing thestructure 272.

As FIG. 49C shows, the physician advances the anchoring branch 276 alongthe guide wire 306 into the anchor site. The anchoring branch 276provides a support to place the operative branch 274 in contact withtissue in the vicinity of the anchor site.

Radiopaque makers 326 can be placed at preestablished positions on thestructure 272 for visualization under fluoroscopy, to thereby aid inguiding the structure 272 to the proper location and orientation.

FIG. 55 shows an alternative embodiment of the anchoring branch 276. Inthis embodiment, the anchoring branch 276 carries an inflatable balloon346 on its distal end. The balloon 346 is inflated to secure theattachment of the anchoring branch 276 to the targeted vessel or cavityanchor site. The anchoring branch 276 includes a lumen 352 that extendsthrough the balloon 346, having an inlet 348 at the distal end of theballoon 346 and an outlet 350 at the proximal end of the balloon 346.The lumen 352 allows blood to flow through the targeted vessel or cavityanchor site, despite the presence of the anchoring balloon 346. Thelumen 306 also allows passage of the guide wire 306 for guiding theanchoring branch 276 into position.

As FIG. 46 shows, the operative branch 274 can carry one or moresteering wires 310 coupled to a bendable spring 312. Coupled to anaccessible control 314, e.g. on the handle 18, pulling on the steeringwires 310 bends the spring 312, in generally the same fashion that thesteering wires 66 affect bending of the spring 64, as previouslydescribed with reference to FIG. 2A. The physician is thereby able toaffirmatively bend the operative branch 274 relative to the anchoringbranch 276 to enhance site access and tissue contact. The steering wires310 can be coupled to the spring 312 to affect bending in one plane orin multiple planes, either parallel to the catheter axis 292 or notparallel to the axis 292.

Alternatively, or in combination with the manually bendable spring 312,the spline element 282 can be prebent to form an elbow (like elbow 70shown in FIG. 11 in association with the structure 20) generallyorthogonal or at some other selected angle to the axis 292 of thecatheter tube 12. The spline element 282 can also be prebent into acircular or elliptical configuration. For example, a circularconfiguration can be used to circumscribe the pulmonary veins in theleft atrium.

Alternatively, or in combination with a bendable operative branch 274,the distal end 16 of the catheter tube 12 can include an independentsteering mechanism (see FIG. 49C), e.g., including a bendable wire 64and steering wires 66, as previously described and as also shown in FIG.2A. By steering the entire distal end 16, the physician orients thebranched structure 272 at different angles relative to the targetedanchor site.

B. Slotted Branch Structures

FIG. 51 shows an embodiment of a branched structure 272, in which theoperative branch 274 can be moved in an outward direction (arrow 316)and an inward direction (arrow 318) relative to the catheter tube 12. Inthis embodiment, the operative branch 274 comprises a tubular body 322,which slidably extends through a lumen 324 in the catheter tube 12. Anaccessible control 328 on the proximal end of the body 322 guides thesliding movement.

The spline element 282, insulating sleeve 284, and operative elements(i.e., electrode elements 28), already described, are carried at thedistal end of the slidable body 322. The catheter tube 12 includes aslot 320 near the distal end 16, through which the slidable body 322passes during outward and inward movement 316 and 318.

The ability to move the operative branch 274 outside the catheter tube12 enables the physician to define the number of electrodes 28contacting the tissue, and thereby define the length of the resultinglesion. Alternatively, a movable operative branch 274 allows thephysician to drag a selected activated electrode element 28 alongtissue, while the anchoring branch 276 provides a stationary point ofattachment.

The slidable body 322 can also be attached and arranged for rotation(arrows 352 in FIG. 51) with respect to the catheter tube 12, ifdesired, by making the exterior contour of the slidable body 322 and theinterior of the lumen 324 matching and symmetric. Rotation of theslidable body 322 can be prevented or restricted, if desired, byproviding an exterior contour for the slidable body 322 that isasymmetric, and sliding the body 322 through a matching asymmetricanchor or lumen within the slot 320 or within the catheter tube 12.

As FIG. 51 shows, radiopaque makers 326 are placed near the slot 320 andnear the distal tip of the operative element 274 for visualization underfluoroscopy. The markers 326 can be located at other parts of thestructure 274, as well, to aid in manipulating the operative branch 274and anchoring branch 276.

The operative branch 274 shown in FIG. 51 can include a steering springand steering wires in the manner previously shown and described in FIG.46. All other mechanisms also previously described to bend the operativebranch 274 in planes parallel and not parallel to the catheter axis 292can also be incorporated in the FIG. 51 embodiment.

FIG. 52 shows an embodiment, like FIG. 51, except that the catheter body12 also carries an accessible control 330 to rotate the slot 320 aboutthe catheter tube axis 292 (arrows 352 in FIG. 52). If the operativebranch 274 is free to rotated upon itself (as previously described), andif the spline element 282 within the operative branch 274 is circular incross section, the operative branch 274 will rotate upon itself duringrotation of the slot 320. In this arrangement, rotation of the slot 320torques the operative branch about the catheter tube axis 292.

On the other hand, if the spline element 282 within the operative branch274 is rectangular in cross section, the operative branch 274 willrotate upon itself during rotation of the slot 320, provided thatrotation of the operative branch 274 about its axis is not prevented,and provided that the angle (a in FIG. 52) between the axis 332 of theoperative branch 274 and the axis 292 of the catheter tube 12 is lessthan 200. Otherwise, an operative branch 274 with a rectilinear splineelement 282, will not rotate upon itself during rotation of the slot320, and thus can not be torqued by rotation of the slot 320.

FIG. 53 shows an embodiment of the structure 272, which like FIG. 51,allows movement of the operative branch 274 through a slot 320. Unlikethe embodiment in FIG. 51, the embodiment shown in FIG. 53 includes apull wire 334 attached to the distal end 336 of the operative branch274. The pull wire 334 passes through the exterior sheath 304 or throughthe catheter tube 12 (previously described) to an accessible stop 336.Advancing the operative branch 274 forward (arrow 338) through the slot320, while holding the pull wire 334 stationary, bends the operativebranch 274 into a loop, in much the same manner previously described inconnection with the FIG. 15A embodiment. Pulling on the wire 334 (arrow342) reduces the amount of exposed length beyond the distal end of thesheath 304. By advancing the catheter tube (arrow 340), the radius ofcurvature of the looped operative branch 274 can be adjusted, in muchthe same way previously shown in the FIG. 17A embodiment.

FIG. 54 shows an embodiment of the structure 272, which like FIG. 51,allows movement of the operative branch 274 through a slot 320. Unlikethe embodiment in FIG. 51, the embodiment shown in FIG. 53 includes aflexible joint 344 which joins the distal end 336 of the operativebranch 274 to the distal end 16 of the catheter tube 12. Advancing theoperative branch 274 forward (arrow 338) through the slot 320, bends theoperative branch 274 into a loop, in much the same manner previouslydescribed in connection with the FIGS. 3 and 15 embodiments. Theflexible joint 344 can comprise a plastic material or a metal material,as the preceding FIGS. 3 and 15 embodiments demonstrate.

C. Spanning Branch Structures

FIG. 56 shows a self-anchoring multiple electrode structure 356comprising multiple operative branches (two operative branches 358 and360 are shown in FIG. 56). Like the operative branch 274 shown in FIG.45, each operative branch 358 and 360 carries one or more operativeelements, which can take various forms, and which in the illustratedembodiment comprise the electrode elements 28. Each operative branch 358and 360 likewise comprises a spline element 362 enclosed within anelectrically insulating sleeve 364, on which the electrode elements 28are carried.

In the illustrated embodiment, the operative branches 358 and 360 arejointly carried within a catheter sheath 370. Each operative branch 358and 360 is individually slidable within the sheath 370 between adeployed position (FIG. 56) and a retracted position (FIG. 57). Itshould be appreciated that each operative branch 358 and 360 can bedeployed and retracted in an individual sheath.

Each operative element 358 and 360 includes a distal region,respectively 366 and 368, which are mutually bent outward in a“bow-legged” orientation, offset from the main axis 372 of the sheath370. This outwardly bowed, spaced apart relationship between the regions366 and 368 can be obtained by prestressing the spline elements 362 intothe desired shape, or by providing a spring which is actively steered bysteering wires (as described numerous times before), or both. Thedesired mutual orientation of the branches 358 and 360 can be retainedby making at least the proximal portion of the spline elements 362 notround, thereby preventing relative rotation of the branches 358 and 360within the sheath 370.

In use (see FIG. 58), each distal region 366 and 368 is intended to beindividually maneuvered into spaced apart anchoring sites, e.g., thepulmonary veins (PV in FIG. 58). Once both regions 366 and 368 aresuitably anchored, the operative branches 360 and 362 are advanceddistally, toward the anchoring sites. The operative branches 360 and 362bend inward, toward the sheath axis 372, to place the electrode elements28 in contact with tissue spanning the anchoring sites.

FIG. 59 shows an alternative embodiment of a self-anchoring structure374. Like the structure 356 shown in FIG. 56, the structure 374 includestwo branches 376 and 378, which are slidably carried within a sheath380. When deployed outside the sheath 380, the distal ends 384 and 386of the branches 376 and 378 are located in an outwardly bowedorientation relative to the axis 388 of the sheath 380. As earlierdescribed in connection with the FIG. 45 embodiment, the branches 376and 378 can be bent outwardly either by prestressing the associatedinterior spline elements 380, located in the branches 376 and 378, orproviding active steering, or both.

In FIG. 59, a flexible element 382 spans the distal ends 384 and 386 ofthe branches 376 and 378. The flexible element 382 is made of materialthat is less rigid that the two branches 376 and 378. In the illustratedembodiment, the flexible element 382 is biased to assume a normallyoutwardly bowed shape, as FIG. 59 shows. The element 382 carries one ormore operative elements, which can vary and which in the illustratedembodiment comprise electrode elements 28.

As FIG. 60 shows, in use, each distal region 384 and 386 is intended tobe individually maneuvered into spaced apart anchoring sites, e.g., thepulmonary veins (PV in FIG. 60). When the regions 384 and 386 aresuitably anchored, the spanning element 382 places the electrodeelements 28 in contact with tissue spanning the anchoring sites. If thetissue region between the anchoring sites has a concave contour (and nota convex contour, as FIG. 60 shows), the outwardly bowed bias of theflexible element 382 will conform to the concave contour, just as itconforms to a convex contour.

D. Spring-Assisted Branch Structures

FIG. 61 shows another embodiment of a spring-assisted multiple electrodestructure 390. The structure 390 includes two operative branches 392 and394 carried at the distal end 16 of the catheter tube 12. The cathetertube 12 forms part of a probe 10, as shown in FIG. 1.

As previously described in connection with the embodiment shown in FIG.56, each operative branch 392 and 394 comprises a spline element 396enclosed within an electrically insulating sleeve 398. Operativeelements, for example, electrode elements 28, are carried by the sleeve398.

In the FIG. 61 embodiment, the spline elements 396 are preformed to movealong the exterior of the distal catheter end 16 and then extendradially outward at an angle of less than 90°. The spline elements 396,prestressed in this condition, act as spring mechanisms for theoperative branches 392 and 394. The prestressed spline elements 396 holdthe branches 392 and 394 in a spaced apart condition (shown in FIG. 61),but resisting further or less radial separation of the branches 392 and394.

A sheath 400 is slidable in a forward direction (arrow 402 in FIG. 62)along the catheter tube 12 to press against and close the radial spacingbetween the branches 392 and 394. This low profile geometry (shown inFIG. 62) allows introduction of the structure 390 into the selected bodyregion. Rearward movement of the sheath 400 (arrow 404 in FIG. 61) freesthe branches 392 and 394, which return due to the spring action of thespline elements 396 to a normally spaced apart condition (shown in FIG.61).

The catheter tube 12 includes an interior lumen 406. As FIG. 61 shows,the lumen 406 accommodates passage of a guide wire 408 with a bluntdistal end 410.

When deployed in an atrium (as FIG. 63A depicts) the distal end 410 ofthe guide wire 408 is maneuvered into a selected anchoring site (e.g., apulmonary vein in the left atrium, or the inferior vena cava in theright atrium). The structure 390, enclosed within the sheath 400, isslid over the guide wire 408 to the targeted site (arrow 412 in FIG.63A). As FIG. 63B shows, the sheath 400 is moved rearwardly (arrow 414in FIG. 63B) to free the spring-like operative branches 392 and 394.Advancing the operative branches 392 and 394 along the guide wire 408opens the radial spacing between the branches. The spring action of thespline elements 396 resisting this action exerts force against thetissue, assuring intimate contact between the electrode elements 28 andthe tissue. The spline elements 396 can also be deployed within anatrium without use of a guide wire 408.

One or more spring-assisted spline elements 396 of the kind shown inFIG. 61 can also be deployed in a ventricle or in contact with theatrial septum for the purpose of making large lesions. As in the atrium,use of the guide wire 408 is optional. However, as shown in FIG. 63C, inthese regions, a guide wire 408 can be used, which includes at itsdistal end a suitable positive tissue fixation element 542, e.g., ahelical screw or vacuum port, to help stabilize the contact between thespline elements 396 and myocardial tissue. Several spline elements 396can be arranged in a circumferentially spaced star pattern to cover alarge surface area and thereby make possible the larger, deeper lesionsbelieved to be beneficial in the treatment of ventricular tachycardia.

The spring action (i.e., spring constant) of the spline elements 396 canbe varied, e.g., by changing the cross sectional area of the splineelements 396, or by making material composition or material processingchanges.

E. Self-Anchoring Loop Structures

FIG. 66 shows an assembly 450, which, in use, creates a self-anchoringloop structure 452 (which is shown in FIG. 68). The assembly 450includes a catheter 486 comprising a flexible catheter tube 454 with ahandle 256 on its proximal end, and which carries a multiple electrodearray 458 on its distal end 470.

In the illustrated embodiment, the multiple electrode array 458comprises electrode elements 28 attached to a sleeve 460 (see FIG. 69),which is made from an electrically insulating material, as alreadydescribed.

As FIG. 69 best shows, a bendable spring 462 is carried within thesleeve 460 near the distal end 470 of the catheter tube 454. One or moresteering wires 464 are attached to the spring 462 and pass through thecatheter tube 454 to a steering controller 468 in the handle. Whilevarious steering mechanisms can be used, in the illustrated embodiment,the controller 468 comprises a rotatable cam wheel of the type shown inLundquist and Thompson U.S. Pat. No. 5,254,088, which is alreadyincorporated into this Specification by reference.

Operation of the steering controller 468 pulls on the steering wires 464to apply bending forces to the spring 462. Bending of the spring 462bends (arrows 490 in FIG. 66) the distal end 470 of the catheter tube454 (shown in phantom lines), to deflect the multiple electrode array458. As heretofore described, the catheter 486 can comprise aconventional steerable catheter.

The catheter tube 454 carries a sheath 472. The sheath 472 includes aproximal gripping surface 482 accessible to the physician. The sheath472 also includes a closed distal end 476, and a slot 474, which is cutout proximal to the closed distal end 476. A region 480 of the sheathremains between the distal edge of the slot 474 and the closed distalcatheter tube end 476. This region 480 peripherally surrounds aninterior pocket 478.

The catheter tube 12 is slidable within the sheath 472. When the distalend 470 occupies the slot 474, sliding the catheter tube 12 forwardinserts the distal end 470 into the pocket 478, as FIG. 67 shows. Thedistal end 470 of the catheter tube 454 can be inserted into the pocket478 either before introduction of the electrode array 458 into thetargeted body region, or after introduction, when the electrode array458 is present within the targeted body region. The pocket 478 is sizedto snugly retain the inserted end 470 by friction or interference.

By holding the sheath 472 stationary and applying a rearward slidingforce on the catheter tube 454, the physician is able to free the distalcatheter tube end 470 from the pocket 478, as FIG. 66 shows. With thedistal end 470 free of the pocket 478, the physician is able to slidethe entire catheter tube 454 from the sheath 472, if desired, and inserta catheter tube of another catheter in its place.

Once the distal catheter tube end 470 is inserted into the pocket 478,the physician can form the loop structure 452. More particularly, bygripping the surface 482 to hold the sheath 472 stationary, thephysician can slide the catheter tube 454 forward with respect to thesheath 472 (arrow 484 in FIG. 68). As FIG. 68 shows, advancement of thecatheter tube 454 progressively pushes the multiple electrode array 458outward through the slot 474. With the distal end 470 captured withinthe pocket 478, the pushed-out portion of the electrode array 458 bendsand forms the loop structure 452.

In many respects, the loop structure 452 shown in FIG. 68 sharesattributes with the loop structure 20, shown in FIG. 3A. The sheathregion 488 underlying the slot 474 serves as a flexible joint for theloop structure 452, just as the flexible joint 44 does for the loopstructure 20 in FIG. 3A. However, unlike the structure 20 in FIG. 3A,the physician is able to mate with the pocket 478 a catheter of his/herown choosing, since the pocket 478 allows easy insertion and removal ofa catheter from the assembly 450. The physician is thereby given theopportunity to select among different catheter types and styles for usein forming the loop structure 452.

Furthermore, as FIG. 70 shows, the distal end 470 of the catheter tube454, when retained within the pocket 478, can serve to establish contactwith an anatomic structure S, while the loop structure 452 contactsnearby tissue T. As FIG. 67 shows, operation of the steering controller468 serves to deflect the pocket region 480 of the sheath 472 along withthe distal catheter tube end 470, to help maneuver and locate the sheathdistal end 470 in association with the anatomic structure S. The distalend 470 of the catheter tube 454, retained within the pocket 478, canthereby serve to stabilize the position of the loop structure 452 incontact with tissue T during use.

The stiffness of the sheath 472 and the length of the flexible jointregion 488 are selected to provide mechanical properties to anchor theloop structure 452 during use. Generally speaking, the sheath 472 ismade from a material having a greater inherent stiffness (i.e., greaterdurometer) than the structure 452 itself. The selected material for thesheath 472 can also be lubricious, to reduce friction during relativemovement of the catheter tube 454 within the sheath 472. For example,materials made from polytetrafluoroethylene (PTFE) can be used for thesheath 452. The geometry of the loop structure 452 can be altered byvarying the stiffness of the sheath 472, or varying the stiffness or thelength of the flexible joint 488, or one or more of these at the sametime.

There are various ways to enhance the releasable retention force betweenthe distal catheter tube end 470 and the pocket 478. For example, FIG.71 shows a sheath having a pocket region 480 in which the interior walls500 of the pocket 478 are tapered to provide a releasable interferencefit about the distal catheter tube end 470. As another example, FIG. 72shows a distal catheter tube end 470, which includes a ball-nose fixture502 which makes releasable, snap-fit engagement with a matingcylindrical receiver 504 formed in the pocket 478. By providing activeattachment mechanisms within the pocket 478, the effective length of thepocket region 480 can be reduced. These preformed regions can be formedby thermal molding.

FIG. 73 shows a modification of the self-anchoring loop structure 452shown in FIG. 68, in which the distal end 470 of the catheter tube 454forms a pivoting junction 506 with the pocket region 480 of the sheath472. FIGS. 74 and 75 show the details of one embodiment of the pivotingjunction 506.

As FIG. 74 shows, the pocket region 480 includes an axial groove 508that opens into the pocket 478. The distal end 470 of the catheter tubeincludes a ball joint 510. As FIG. 75 shows, forward sliding movement ofthe catheter tube 454 advances the distal end 470, including the balljoint 510, into the pocket 478. As FIG. 76 shows, as further advancementof the catheter tube 454 progressively pushes the multiple electrodearray 458 outward through the slot 474, the ball joint 510 enters thegroove 508. The ball joint 510 pivots within the groove 508, therebyforming the pivoting junction 506. The junction 506 allows-the distalend 470 to swing with respect to the pocket region 480 (arrows 512 inFIG. 76), as the pushed-out portion of the electrode array 458 bends andforms the loop structure 452, shown in FIG. 73.

FIGS. 77 A to 77D show another embodiment of the pivoting junction 506.In this embodiment, a separately cast plastic or metal cap 514 isattached to the end of the sheath 472. The cap 514 includes an interiorcavity forming the pocket 478. Unlike the previously describedembodiments, the pocket 478 in the cap 514 includes an interior wall 516(see FIG. 77D), which is closed except for a slotted keyway 518.

The cap 514 includes the previously described groove 508. Unlike theprevious embodiments, the groove 508 extends to and joins the slottedkeyway 518 (see FIG. 77A). The groove 508 also extends through thedistal end 520 of the cap 514 to an opening 522 (see FIG. 77B) on theside of the cap 514 that faces away from the sheath slot 474. As FIG.77B shows, the opening 522 accommodates passage of the ball joint 510carried at the distal end 470 of the catheter tube 454. Advancing theball joint 510 from the opening 522 along the groove 508 locks the balljoint 510 within the pocket 478. Further advancement brings the balljoint 510 to rest within the slotted keyway 518 (see FIG. 77C). Theslotted keyway 518 retains the ball joint 510, securing the distalcatheter tube end 470 to the cap 514. The interference between the balljoint 510 and the keyway 518 prevents separation of the distal cathetertube end 470 from the sheath 472 by sliding axial movement of thecatheter tube 545 within the sheath 472. However, as FIG. 77D shows, theball joint 510 pivots within the groove 508 of the cap 514, therebyforming the pivoting junction 506, to allow the distal end 470 to swingwith respect to the pocket region 478.

The distal catheter tube end 470 is separated from the cap 514 bysliding the ball joint 510 along the groove 508 into the opening 522.The ball joint 510 passes through the opening 522, thereby releasing thecatheter tube 454 from the sheath 472.

FIGS. 78A to 78C show another embodiment of the pivoting junction 506.In this embodiment, like FIGS. 77A to 77D, a separately cast plastic ormetal cap 606 is attached to the end of the sheath 472. The cap 606includes an interior cavity forming the pocket 608. As FIG. 78A shows,the pocket 608 receives the ball joint 510 (carried by the distal loopstructure end 470) through the sheath end 612 of the cap 606, in themanner previously described and shown with reference to FIG. 76.

As FIGS. 78B and 78C show, the ball joint 510 pivots within the pocket608 through a groove 610 formed in the cap 606. The pivoting junction506 is thereby formed, which allows the distal end 470 to swing withrespect to the cap 606.

Other exemplary embodiments of the pivoting junction are illustrated inFIGS. 94-101. Referring first to FIGS. 94-96, a pivoting junction isformed by a pivot assembly 614 that is secured to the distal end of thesheath 472. The pivot assembly 614 includes a base member 616 and apivot member 618 which pivots relative to the base member. In theembodiment shown in FIGS. 94-96, the pivot member 618 consists of a ball620, a connector 622 (such as the illustrated threaded connector) forsecuring the distal end 470 of the catheter tube to the pivot assembly,and a neck member 624 which links the ball to the connector. The ball620 is inserted into a socket opening 626 during assembly and is held inplace with a pin 628. The pin 628 reduces the size of the outer portionof the socket opening 626 to a size that is less than the diameter ofthe ball 620, thereby preventing escape of the ball from the socketopening while allowing the ball to rotate. Use of a removable pin 628 tosecure the ball 620 in place allows the operative portion of thecatheter tube 454 (i.e. the portion which includes the electrodeelements 28) to be removed for use in other types of catheters.Alternatively, the socket opening 626 may be closed after assembly topermanently hold the ball 620 in place. This provides superiormaintenance of the loop over the course of repeated manipulations of thecatheter tube 454.

As shown by way of example in FIGS. 94-96, the pivot member 618 pivotsthrough a slot 630 that is formed in the base member 616. The slot 630is connected to the socket opening 626 in the illustrated embodiment.When the catheter tube 454 slides through the interior bore 632 of thesheath 472 in the distal direction, the pivot member 618 pivots throughthe slot 630 and a portion of the catheter tube is forced through thesheath slot 474. As a result, a loop is formed which exerts a force onthe endocardial surface of interest. Here, the loop includes electrodeelements 28.

In the exemplary embodiment shown in FIGS. 95 and 96, the neck member624 is cylindrically-shaped (i.e. round in cross-section). This allowsthe pivot member 618 to rotate in the directions shown by arrow 634 inFIG. 95, if necessary, as the pivot member pivots through the slot 630.Such rotation allows the catheter tube 454 generally, and the operativeportion in particular, to rotate with respect to the pivot assembly 614.However, as shown by way of example in FIG. 97, the shape of a neckmember 636 and the walls which define the slot 630 may be such thatrotation of the pivot member 618 is prevented. The sides of the neckmember 636 are planar, as are the side walls of the slot 630, and thereis a close fit between the neck member and the side walls. Of course,many other combinations of neck member and slot wall shapes may be usedto produce the desired results. For example, rotation of the cathetertube 454 relative to the pivot assembly 614 can also be preventedthrough the use of the exemplary pivot member 638 shown in FIG. 98.Here, a rectangular member 640 replaces the above-described ball andneck assembly. A pin 642, about which the rectangular member 640 pivots,passes through a hole (not shown) on the distal end of the rectangularmember. The pin 642 can be secured to the base member 616 by spotwelding, adhesive, or other suitable means. Should minimal rotation bedesired, a neck member may, for example, shaped such that i iselliptical in cross-section and oriented such that its major axis isaligned with the slot 630.

As described above with reference to FIGS. 7A-9, the length and shape ofthe slot in the sheath 474 may be varied in order to produce the desiredloop configuration. For example, a more lateral loop will be produced bya relatively longer slot 474, while a more distal loop will be producedby a relatively shorter opening. Still other methods of influencing theloop configuration are discussed above with reference to, for example,FIGS. 11, 12. 40, 41 and 43.

In the illustrated embodiments, the pivot member 618 is free to rotatefrom the orientation shown in FIG. 96, which is aligned with thelongitudinal axis 644 of the sheath, to an orientation that isapproximately 270 degrees from the longitudinal axis (note arrow 646 inFIG. 94). This range may be decreased by adding a second pin that isused solely to prevent movement of the pivot member 618. For example, apin may be added to the distal end of the base member 616 such that itextends across the slot 630 and limits the rotation of the pivot member218 to approximately 180 degrees.

Another exemplary embodiment of the present invention is illustrated inFIGS. 99 and 100. Here, a self-anchoring pivot assembly 648. includes arectangular pivot member 650 and a base member 652. A length of sheathmaterial 654 extends distally from the base member 652 and forms ananchor point. The anchor point may be used to secure the distal end ofthe catheter into the superior vena cava (as shown in FIG. 100),pulmonary vein, or any other appropriate vessel, appendage or cavity. Aguide wire 656 could also be used as a guide and anchor for thepulmonary vein. The base member 652 includes a slot 658 which limitsrotation of the pivot member 650 to approximately 90 degrees. However,the slot may be reconfigured to increase the possible range of rotationto 180 degrees.

With respect to materials, the pivot assemblies are preferably formedfrom injection molded plastic or metal (such as stainless steel) that ismachined to the desired configuration. This results in a relativelystiff joint which prevents torquing of the operative portion of thecatheter tube 454 relative to the sheath. As illustrated for example inFIG. 101, the stiffness of the sheath may be increased by, for example,attaching metallic or polymeric support structures 660 to the sheath.The support structures 660 may secured to the inner (as shown) or outersurfaces of the sheath with mechanical fasteners or adhesives. One ormore support structures 660 can also be imbedded in the sheath materialin, for example, the manner described above with reference to FIGS. 3Band 3C. Additionally, although the support structures are orientedlongitudinally in the illustrated embodiment, differently orientedsupport structures may be added, or the orientation of the supportstructures may be changed to increase stiffness in other directions.

In the exemplary embodiment shown in FIG. 94, the sheath 472 andoperative portion of the catheter tube 454 are both circular incross-section. Thus, the operative portion of the catheter tube 454 canbe rotated relative to the sheath and torsional forces may be applied tothe catheter tube without imparting those same forces to the sheath.However, an elliptically keyed interference arrangement (such as thatshown in FIG. 13A) may be employed to prevent rotation of the cathetertube 454 relative to the sheath 472. The outer surface of catheter tubeand inner surface of the sheath may also be configured in, for example,the manner shown in FIG. 13B so that a predefined range of relativerotation will be permitted.

F. Deployment and Use of Self-Anchoring Multiple Electrode Structures

1. Left Atrium

The self-anchoring multiple electrode structures described above can bedeployed into the left atrium to create lesions between the pulmonaryveins and the mitral valve annulus. Tissue nearby these anatomicstructures are recognized to develop arrhythmia substrates causingatrial fibrillation. Lesions in these tissue regions block reentry pathsor destroy active pacemaker sites, and thereby prevent the arrhythmiafrom occurring.

FIG. 79 shows (from outside the heart H) the location of the majoranatomic landmarks for lesion formation in the left atrium. Thelandmarks include the right inferior pulmonary vein (RIPV), the rightsuperior pulmonary vein (RSPV), the left superior pulmonary vein (LSPV),the left inferior pulmonary vein (LIPV); and the mitral valve annulus(MVA). FIGS. 80A to FIGS. 80D show representative lesion patterns formedinside the left atrium based upon these landmarks.

In FIG. 80A, the lesion pattern comprises a first leg L1 between theright inferior pulmonary vein (RIPV) and the right superior pulmonaryvein (RSPV); a second leg L2 between the RSPV and the left superiorpulmonary vein (LSPV); a third leg L3 between the left superiorpulmonary vein (LSPV) and the left inferior pulmonary vein (LIPV); and afourth leg L4 leading between the LIPV and the mitral valve annulus(MVA).

FIG. 80B shows an intersecting lesion pattern comprising horizontal legL1 extending between the RSPV-LSPV on one side and the RIPV-LIPV on theother size, intersected by vertical leg L2 extending between theRSPV-RIPV on one side and the LSPV-LIPV on the other side. The secondleg L2 also extends to the MVA.

FIG. 80C shows a criss-crossing lesion pattern comprising a first legextending between the RSPV and LIPV; a second leg L2 extending betweenthe LSPV and RIPV; and a third leg L3 extending from the LIPV to theMVA.

FIG. 80D shows a circular lesion pattern comprising a leg L1 thatextends from the LSPV, and encircles to RSPV, RIPV, and LIPV, leadingback to the LSPV.

The linear lesion patterns shown in FIGS. 80A, 80B, and 80C can beformed, e.g., using the structure 272 shown in FIGS. 45 and 46, byplacing the anchoring branch 276 in a selected one of the pulmonaryveins to stabilize the position of the operative branch 274, and thenmaneuvering the operative branch 274 to sequentially locate it along thedesired legs of the lesion pattern. It may be necessary to relocate theanchoring branch 276 in a different pulmonary vein to facilitatemaneuvering of the operative branch 274 to establish all legs of thepattern. The branched structures 356 (FIG. 56) or 374 (FIG. 59) can alsobe used sequentially for the same purpose, in the manner shown in FIG.58 (for structure 356) and FIG. 60 (for structure 374).

The circular lesion pattern shown in FIG. 80D can be formed, e.g., usingan anchored loop structure 458 as shown in FIGS. 68 or 73. Using thesestructures, the distal end 470 of the catheter tube 454 (enclosed withinthe pocket 478) is located within a selected one of the pulmonary veins(the LSPV in FIG. 80D), and the loop structure is advanced from thesheath 472 to circumscribe the remaining pulmonary veins. As with otherloop structures, the loop structure tend to seek the largest diameterand occupy it. Most of the structures are suitable for being torqued orrotated into other planes and thereby occupy smaller regions. Theanchored loop structure 458 is also suited for forming lesion legs thatextend from the inferior pulmonary veins to the mitral valve annulus(for example, L4 in FIG. 80A and L3 in FIG. 80C).

To access the left atrium, any of these structures can be introduced inthe manner shown in FIG. 44 through the inferior vena cava (IVC) intothe right atrium, and then into the left atrium through a conventionaltranseptal approach. Alternatively, a retrograde approach can beemployed through the aorta into the left ventricle, and then through themitral valve into the left atrium.

2. Right Atrium

FIG. 79 shows (from outside the heart H) the location of the majoranatomic landmarks for lesion formation in the right atrium. Theselandmarks include the superior vena cava (SVC), the tricuspid valveannulus (TVA), the inferior vena cava (IVC), and the coronary sinus(CS). Tissue nearby these anatomic structures have been identified asdeveloping arrhythmia substrates causing atrial fibrillation. Lesions inthese tissue regions block reentry paths or destroy active pacemakersites and thereby prevent the arrhythmia from occurring.

FIGS. 81A to 81C show representative lesion patterns formed inside theright atrium based upon these landmarks.

FIG. 81A shows a representative lesion pattern L that extends betweenthe superior vena cava (SVC) and the tricuspid valve annulus (TVA). FIG.81B shows a representative lesion pattern that extends between theinterior vena cava (IVC) and the TVA. FIG. 81 C shows a representativelesion pattern L that extends between the coronary sinus (CS) and thetricuspid valve annulus (TVA).

The self-anchoring multiple electrode structures described above can bedeployed into the right atrium to create these lesions. For example, thestructure 272 shown in FIGS. 45 and 46 can be used, by placing theanchoring branch 276 in the SVC or IVC to stabilize the position of theoperative branch 274, and then maneuvering the operative branch 274 tolocate it along the desired path of the lesion pattern. The branchedstructures 356 (FIG. 56) or 374 (FIG. 59) can also be used sequentiallyfor the same purpose, in the manner shown in FIG. 58 (for structure 356)and FIG. 60 (for structure 374).

Any of these structures can be introduced in the manner shown in FIG. 44through the inferior vena cava (IVC) into the right atrium.

3. Epicardial Use

Many of the structures suited for intracardiac deployment, as discussedabove, can be directly applied to the epicardium through conventionalthoracotomy or thoracostomy techniques. For example, the structuresshown in FIGS. 56, 59, 61, 66, and 73 are well suited for epicardialapplication.

III. Flexible Electrode Structures

A. Spacing of Electrode Elements

In the illustrated embodiment, the size and spacing of the electrodeelements 28 on the various structures can vary.

1. Long Lesion Patterns

For example, the electrode elements 28 can be spaced and sized forcreating continuous, long lesion patterns in tissue, as exemplified bythe lesion pattern 418 in tissue T shown in FIG. 64. Long, continuouslesion patterns 418 are beneficial to the treatment of atrialfibrillation. The patterns 418 are formed due to additive heatingeffects, which cause the lesion patterns 418 to span adjacent, spacedapart electrode 28, creating the desired elongated, long geometry, asFIG. 64 shows.

The additive heating effects occur when the electrode elements 28 areoperated simultaneously in a bipolar mode between electrode elements 28.Furthermore, the additive heating effects also arise when the electrodeelements 28 are operated simultaneously in a unipolar mode, transmittingenergy to an indifferent electrode 420 (shown in FIG. 44).

More particularly, when the spacing between the electrodes 28 is equalto or less than about 3 times the smallest of the diameters of theelectrodes 28, the simultaneous emission of energy by the electrodes 28,either bipolar between the segments or unipolar to the indifferentelectrode 420, creates an elongated continuous lesion pattern 58 in thecontacted tissue area due to the additive heating effects.

Alternatively, when the spacing between the electrodes along thecontacted tissue area is equal to or less than about 2 times the longestof the lengths of the electrodes 28, the simultaneous application ofenergy by the electrodes 28, either bipolar between electrodes 28 orunipolar to the indifferent electrode 420, also creates an elongatedcontinuous lesion pattern 58 in the contacted tissue area due toadditive heating effects.

Further details of the formation of continuous, long lesion patterns arefound in copending U.S. patent application Ser. No. 08/287,192, filedAug. 8, 1994, entitled “Systems and Methods for Forming Elongated LesionPatterns in Body Tissue Using Straight or Curvilinear ElectrodeElements,” which is incorporated herein by reference.

Alternatively, long continuous lesion patterns, like that shown in FIG.64, can be achieved using an elongated electrode element made from aporous material. By way of illustration, FIG. 82 shows a loop electrodestructure 424, like that shown in FIG. 2A. The structure 424 includes anelectrode body 428, which includes a porous material 430 to transferablation energy by ionic transport.

As FIG. 82 shows, the distal end 426 of the electrode body 428 iscoupled to a flexible joint 440, which is part of the slotted sheath442, as previously described in connection with FIG. 3A. Advancement ofthe electrode body 428 from the slotted sheath 442 creates the loopstructure 424, in the same manner that the loops structure 20 shown inFIG. 3A is formed.

As best shown in FIG. 83, the electrode body 428 includes a centersupport lumen 432 enveloped by the porous material 430. The lumen 432carries spaced-apart electrodes 429 along its length. The lumen 432 alsoincludes spaced-apart apertures 434 along its length.

The lumen 432 includes a proximal end 430, which communicates with asource of ionic fluid 438. The lumen 432 conveys the ionic fluid 438.The ionic fluid 438 passes through the apertures 434 and fills the spacebetween the lumen 432 and the surrounding porous material 430. The fluid438 also serves to expand the diameter of the structure 424. Thestructure 424 therefore possesses a low profile geometry, when no liquid438 is present, for introduction within the targeted body regionenclosed within the slotted sheath 442. Once advanced from the sheath442 and formed into the loop structure 424, fluid 438 can be introducedto expand the structure 424 for use.

The porous material 430 has pores capable of allowing transport of ionscontained in the fluid 438 through the material 430 and into contactwith tissue. As FIG. 83 also shows, the electrodes 429 are coupled to asource 444 of radio frequency energy. The electrodes 429 transmit theradio frequency energy into the ionic fluid 438. The ionic (and,therefore, electrically conductive) fluid 438 establishes anelectrically conductive path. The pores of the porous material 430establish ionic transport of ablation energy from the electrodes 429,through the fluid 438, liquid, to tissue outside the electrode body 428.

Preferably, the fluid 438 possesses a low resistivity to decrease ohmicloses, and thus ohmic heating effects, within the body 428. Thecomposition of the electrically conductive fluid 438 can vary. In theillustrated embodiment, the fluid 438 comprises a hypertonic salinesolution, having a sodium chloride concentration at or near saturation,which is about 5% to about 25% weight by volume. Hypertonic salinesolution has a low resistivity of only about 5 ohm/cm, compared to bloodresistivity of about 150 ohm/cm and myocardial tissue resistivity ofabout 500 ohm/cm.

Alternatively, the composition of the electrically conductive fluid 438can comprise a hypertonic potassium chloride solution. This medium,while promoting the desired ionic transfer, requires closer monitoringof the rate at which ionic transport occurs through the pores of thematerial 430, to prevent potassium overload. When hypertonic potassiumchloride solution is used, it is preferred to keep the ionic transportrate below about 10 mEq/min.

Regenerated cellulose membrane materials, typically used for bloodoxygenation, dialysis, or ultrafiltration, can be used as the porousmaterial 430. Regenerated cellulose is electrically non-conductive;however, the pores of this material (typically having a diameter smallerthan about 0.1 Tm) allow effective ionic transport in response to theapplied RF field. At the same time, the relatively small pores preventtransfer of macromolecules through the material 430, so that pressuredriven liquid perfusion is less likely to accompany the ionic transport,unless relatively high pressure conditions develop within the body 428.

Other porous materials can be used as the porous material 430. Candidatematerials having pore sizes larger than regenerated cellulous material,such as nylon, polycarbonate, polyvinylidene fluoride (PTFE),polyethersulfone, modified acrylic copolymers, and cellulose acetate,are typically used for blood microfiltration and oxygenation. Porous ormicroporous materials may also be fabricated by weaving a material (suchas nylon, polyester, polyethylene, polypropylene, fluorocarbon, finediameter stainless steel, or other fiber) into a mesh having the desiredpore size and porosity. These materials permit effective passage of ionsin response to the applied RF field. However, as many of these materialspossess larger pore diameters, pressure driven liquid perfusion, and theattendant transport of macromolecules through the pores, are also morelikely to occur at normal inflation pressures for the body 428.Considerations of overall porosity, perfusion rates, and lodgment ofblood cells within the pores of the body 128 must be taken more intoaccount as pore size increase.

Low or essentially no liquid perfusion through the porous body 428 ispreferred. Limited or essentially no liquid perfusion through the porousbody 428 is beneficial for several reasons. First, it limits salt orwater overloading, caused by transport of the hypertonic solution intothe blood pool. This is especially true, should the hypertonic solutioninclude potassium chloride, as observed above. Furthermore, limited oressentially no liquid perfusion through the porous body 428 allows ionictransport to occur without disruption. When undisturbed by attendantliquid perfusion, ionic transport creates a continuous virtual electrodeat the electrode body-tissue interface. The virtual electrodeefficiently transfers RF energy without need for an electricallyconductive metal surface.

FIGS. 84 and 85 show an embodiment of the porous electrode body 428which includes spaced-apart external rings 446, which form porouselectrode segments. It is believed that, as the expanded dimension ofthe body 428 approaches the dimension of the interior electrodes 429,the need to segment the electrode body 428 diminishes.

Alternatively, as FIG. 86 shows, instead of a lumen 432 within the body438, a foam cylinder 448 coupled in communication with the ionic fluid438 could be used to carry the electrodes 429 and perfuse the ionicfluid 438.

2. Interrupted Lesion Patterns

The electrode elements 28 can be sized and spaced to form interrupted,or segmented lesion patterns, as exemplified by the lesion pattern 422in tissue T shown in FIG. 65. Alternatively, spaced-apart electrodeelements 28 capable of providing long lesion patterns 418 can beoperated with some electrode elements 28 energized and others not, toprovide an interrupted lesion pattern 422, as FIG. 65 exemplifies.

When the spacing between the electrodes 28 is greater than about 5 timesthe smallest of the diameters of the electrodes 28, the simultaneousemission of energy by the electrodes 28, either bipolar between segmentsor unipolar to the indifferent electrode 420, does not generate additiveheating effects. Instead, the simultaneous emission of energy by theelectrodes 28 creates an elongated segmented, or interrupted, lesionpattern in the contacted tissue area.

Alternatively, when the spacing between the electrodes 28 along thecontacted tissue area is greater than about 3 times the longest of thelengths of the electrodes 28, the simultaneous application of energy,either bipolar between electrodes 28 or unipolar to the indifferentelectrode 420, creates an elongated segmented, or interrupted, lesionpattern.

3. Flexibility

When the electrode elements 28 are flexible, each element 28 can be aslong as 50 mm. Thus, if desired, a single coil electrode element 28 canextend uninterrupted along the entire length of the support structure.However, a segmented pattern of spaced apart, shorter electrode elements28 is preferred.

If rigid electrode elements 28 are used, the length of the eachelectrode segment can vary from about 2 mm to about 10 mm. Usingmultiple rigid electrode elements 28 longer than about 10 mm eachadversely effects the overall flexibility of the element. Generallyspeaking, adjacent electrode elements 28 having lengths of less thanabout 2 mm do not consistently form the desired continuous lesionpatterns.

4. Temperature Sensing

As FIG. 3A shows, each electrode element 28 can carry at least one and,preferably, at least two, temperature sensing elements 540. The multipletemperature sensing elements 540 measure temperatures along the lengthof the electrode element 28. The temperature sensing elements 540 cancomprise thermistors or thermocouples. If thermocouples are used, a coldjunction 24 (see FIG. 3A) can be carried on the same structure as theelectrode elements 28.

An external temperature processing element (not shown) receives andanalyses the signals from the multiple temperature sensing elements 540in prescribed ways to govern the application of ablating energy to theelectrode element 28. The ablating energy is applied to maintaingenerally uniform temperature conditions along the length of the element28.

Further details of the use of multiple temperature sensing elements intissue ablation can be found in copending U.S. patent application Ser.No. 08/286,930, filed Aug. 8, 1994, entitled “Systems and Methods forControlling Tissue Ablation Using Multiple Temperature SensingElements.”

Various features of the invention are set forth in the following claims.

We claim:
 1. A catheter assembly, comprising: a sheath including a sidewall defining an interior bore and a distal end; a bendable cathetertube carried for sliding movement in the interior bore of the sheath,the catheter tube defining a distal tip region; and a pivot assembly,associated with the distal end of the sheath and the distal tip regionof the catheter tube, including a movable member that is movablerelative to the distal end of the sheath.
 2. A catheter assembly asclaimed in claim 1, wherein the side wall of the sheath defines anopening, and the catheter tube is secured to the pivot assembly suchthat the catheter tube will bend outwardly through the opening in theside wall in response to sliding movement of the catheter tube towardthe distal region of the sheath.
 3. A catheter assembly as claimed inclaim 1, wherein the pivot assembly includes a base member and themovable member is movable relative to the base member.
 4. A catheterassembly as claimed in claim 3, wherein the base member and movablemember are formed from substantially rigid material.
 5. A catheterassembly as claimed in claim 1, wherein the movable member pivotsrelative to the distal end of the sheath.
 6. A catheter assembly asclaimed in claim 1, further comprising: at least one operative elementcarried by the catheter tube.
 7. A catheter assembly as claimed in claim6, wherein the at least one operative element includes an electrode. 8.A catheter assembly as claimed in claim 1, wherein the pivot assembly islocated in spaced relation to the distal end of the sheath.
 9. Acatheter assembly, comprising: a sheath including a side wall definingan interior bore and a distal region; a bendable catheter tube carriedfor sliding movement in the interior bore of the sheath, the cathetertube defining a distal region; and a pivot assembly including a basemember and a movable member that is movable relative to the base member,the base member having a socket and the movable member having a balladapted to be received in the socket; the pivot assembly beingassociated with the distal region of the sheath and the distal region ofthe catheter tube such that the movable member is movable relative to atleast one of the distal region of the sheath and the distal region ofthe catheter tube.
 10. A catheter assembly as claimed in claim 9,further comprising: a pin extending across the socket such that the ballis secured within the socket.
 11. A catheter assembly as claimed inclaim 9, wherein the movable member further comprises a connectoradapted to be secured to the distal region of the catheter tube and aneck member extending from the ball to the connector.
 12. A catheterassembly as claimed in claim 9, further comprising: at least oneoperative element carried by the catheter tube.
 13. A catheter assemblyas claimed in claim 12, wherein the at least one operative elementincludes an electrode.
 14. A catheter assembly, comprising: a sheathincluding a side wall defining an interior bore and a distal region; abendable catheter tube carried for sliding movement in the interior boreof the sheath, the catheter tube defining a distal region; and a pivotassembly including a base member and movable member that is movablerelative to the base member, the base member defining a slot throughwhich the movable member moves, and the movable member and base memberslot being configured such that the movable member is substantiallyprevented from rotating when a portion thereof is within the slot; thepivot assembly being associated with the distal region of the sheath andthe distal region of the catheter tube such that the movable member ismovable relative to at least one of the distal region of the sheath andthe distal region of the catheter tube.
 15. A catheter assembly asclaimed in claim 14, further comprising: at least one operative elementcarried by the catheter tube.
 16. A catheter assembly as claimed inclaim 13, wherein the at least one operative element includes anelectrode.
 17. A catheter assembly, comprising: a sheath including aside wall defining an interior bore and a distal region; a bendablecatheter tube carried for sliding movement in the interior bore of thesheath, the catheter tube defining a distal region; and a pivot assemblyincluding a base member and movable member that is movable relative tothe base member and pivotably secured to the base member by a pin; thepivot assembly being associated with the distal region of the sheath andthe distal region of the catheter tube such that the movable member ismovable relative to at least one of the distal region of the sheath andthe distal region of the catheter tube.
 18. A catheter assembly asclaimed in claim 17, further comprising: at least one operative elementcarried by the catheter tube.
 19. A catheter assembly as claimed inclaim 18, wherein the at least one operative element includes anelectrode.
 20. A catheter assembly, comprising: a sheath including aside wall defining a distal region, a distal end, and an interior borewith an inner surface having a shape and a longitudinal axis; a bendablecatheter tube carried for sliding movement in the interior bore of thesheath, the catheter tube defining a distal region, a distal end, alongitudinal axis and an outer surface having a shape; and a pivotassembly associated with the distal region of the sheath and the distalregion of the catheter tube; wherein the respective shapes of the outersurface of the catheter tube and inner surface of the sheath at at leastone location proximally spaced from the distal ends of the catheter tubeand sheath are such that rotation of the catheter tube relative to thesheath about the longitudinal axis of the catheter tube will cause atleast a portion of the outer surface of the catheter tube to engage theinner surface of the sheath when the longitudinal axis of the cathetertube is substantially coincident with the longitudinal axis of theinterior bore at the at least one location.
 21. A catheter assembly asclaimed in claim 20, further comprising: at least one operative elementcarried by the catheter tube.
 22. A catheter assembly as claimed inclaim 21, wherein the at least one operative element includes anelectrode.
 23. A catheter assembly as claimed in claim 20, wherein therespective shapes of the outer surface of the catheter tube and innersurface of the sheath are such that rotation of the catheter tuberelative to the sheath is substantially prevented.
 24. A catheterassembly as claimed in claim 20, wherein the sheath and the cathetertube define respective distal ends and the pivot assembly is adapted toallow the distal end of the catheter tube to pivot at leastapproximately 180 degrees relative to the distal end of the sheath. 25.A catheter assembly, comprising: a sheath including a side wall defininga distal region, a distal end, and an interior bore with an innersurface having a shape and a longitudinal axis; a bendable catheter tubecarried for sliding movement in the interior bore of the sheath, thecatheter tube defining a distal region, a distal end, a longitudinalaxis and an outer surface having a shape; and a pivot assemblyassociated with the distal region of the sheath and the distal region ofthe catheter tube; wherein the outer surface of the catheter tube andinner surface of the sheath are elliptically keyed at at least onelocation proximally spaced from the distal ends of the catheter tube andsheath, and rotation of the catheter tube relative to the sheath aboutthe longitudinal axis of the catheter tube will cause at least a portionof the outer surface of the catheter tube to engage the inner surface ofthe sheath when the longitudinal axis of the catheter tube issubstantially coincident with the longitudinal axis of the interior boreat the at least one location.
 26. A catheter assembly as claimed inclaim 25, further comprising: at least one operative element carried bythe catheter tube.
 27. A catheter assembly as claimed in claim 26,wherein the at least one operative element includes an electrode.
 28. Acatheter assembly, comprising: a sheath including a side wall defining adistal region, a distal end, and an interior bore with an inner surfacehaving a shape and a longitudinal axis; a bendable catheter tube carriedfor sliding movement in the interior bore of the sheath, the cathetertube defining a distal region, a distal end, a longitudinal axis and anouter surface having a shape; and a pivot assembly associated with thedistal region of the sheath and the distal region of the catheter tube;wherein the outer surface of the catheter tube defines a non-circularcross-section in a plane perpendicular to the longitudinal axis of thecatheter tube at at least one location proximally spaced from the distalends of the catheter tube and sheath, the sheath includes an outersurface that defines a circular cross-section in a plane perpendicularto the longitudinal axis of the sheath at the at least one location, androtation of the catheter tube relative to the sheath about thelongitudinal axis of the catheter tube will cause at least a portion ofthe outer surface of the catheter tube to engage the inner surface ofthe-sheath when the longitudinal axis of the catheter tube issubstantially coincident with the longitudinal axis of the interior boreat the at least one location.
 29. A catheter assembly as claimed inclaim 28, further comprising: at least one operative element carried bythe catheter tube.
 30. A catheter assembly as claimed in claim 29,wherein the at least one operative element includes an electrode.
 31. Acatheter, comprising: a sheath including a side wall defining a distalregion, a distal end, and an interior bore with an inner surface havinga shape and a longitudinal axis; a bendable catheter tube carried forsliding movement in the interior bore of the sheath, the catheter tubedefining a distal region, a distal end, a longitudinal axis and an outersurface having a shape; and a pivot assembly associated with the distalregion of the sheath and the distal region of the catheter tube; whereinthe inner surface of the sheath is butterfly shaped at at least onelocation proximally spaced from the distal end of the sheath and therespective shapes of the outer surface of the catheter tube and innersurface of the sheath at the at least one location are such thatrotation of the catheter tube relative to the sheath about thelongitudinal axis of the catheter tube will cause at least a portion ofthe outer surface of the catheter tube to engage the inner surface ofthe sheath when the longitudinal axis of the catheter tube issubstantially coincident with the longitudinal axis of the interior boreat the at least one location.
 32. A catheter assembly as claimed inclaim 31, further comprising: at least one operative element carried bythe catheter tube.
 33. A catheter assembly as claimed in claim 32,wherein the at least one operative element includes an electrode.
 34. Acatheter assembly, comprising: a sheath including a side wall defining alongitudinal axis, an interior bore, a distal end and a distal region; abendable catheter tube carried for sliding movement in the interior boreof the sheath, the catheter tube defining a distal tip region; and apivot assembly, associated with the distal end of the sheath and thedistal tip region of the catheter tube, that allows the distal tipregion of the catheter tube to pivot at least approximately 180 degreesrelative to the distal end of the sheath about an axis substantiallyperpendicular to the distal region of the longitudinal axis of thesheath.
 35. A catheter assembly as claimed in claim 34, wherein thepivot assembly allows the distal region of the catheter tube to pivot atleast approximately 270 degrees relative to the longitudinal axis.
 36. Acatheter assembly as claimed in claim 34, further comprising: at leastone operative element carried by the catheter tube.
 37. A catheterassembly as claimed in claim 36, wherein the at least one operativeelement includes an electrode.
 38. A catheter assembly, comprising: asheath including a side wall defining a distal end, a distal region, adistal end, and an interior bore with a longitudinal axis; a bendablecatheter tube, defining a longitudinal axis, a distal end and a distalregion, carried for sliding movement in the interior bore of the sheath;the sheath and catheter tube further including respective distal regionportions proximally spaced from the respective distal ends that arelongitudinally aligned with one another when the longitudinal axis ofthe interior bore is substantially coincident with the longitudinal axisof the catheter tube; and a pivot assembly associated with the distalregion of the sheath and the distal region of the catheter tube thatallows the distal region portion of the catheter tube to pivot at leastapproximately 180 degrees relative to the distal end of the sheath aboutan axis substantially perpendicular to the distal region of thelongitudinal axis of the interior bore.
 39. A catheter assembly asclaimed in claim 38, wherein the pivot assembly allows the distal regionof the catheter tube to pivot at least approximately 270 degreesrelative to the longitudinal axis.
 40. A catheter assembly as claimed inclaim 38, further comprising: at least one operative element carried bythe catheter tube.
 41. A catheter assembly as claimed in claim 40,wherein the at least one operative element includes an electrode.